Primary voters in the key battleground state of Michigan as well as Missouri, Mississippi, Idaho, North Dakota and Washington state head to the polls in a closely watched contest that could help determine the next phase of the Democratic race for the presidential nomination.

There are 352 delegates up for grabs across the six states.

Stakes are especially high for Vermont Sen. Bernie Sanders, a progressive-standard-bearer who is lagging behind former Vice President Joe Biden in delegates. Sanders is hoping that Michigan will offer a repeat of his 2016 upset when he eked out a win against former Secretary of State of Hillary Clinton-- who was favored to win the state during the primary contests.

Biden, meanwhile, has the wind at his back having netted a number of moderate endorsements. He has pointed to this growing list of such people as former competitors Sen. Cory Booker, D-NJ, and Sen. Kamala Harris, D-Calif as a sign that he is better equipped to take on the White House, arguing that he is the only candidate who can beat Trump.

Here's how the night is unfolding. Please refresh for updates.

6:38 p.m. Biden to speak at 9:30 p.m. in Philadelphia

Following Tuesday night's primary votes, former Vice President Joe Biden will speak at 9:30 p.m. at the National Constitution Center in Philadelphia, according to his campaign.

Biden is currently en route from Cleveland.

ABC News' Political Director Rick Klein reporting

6:12 p.m. Michigan unofficial results aren't expected until Wednesday

The Michigan secretary of state confirmed to ABC News that the complete, unofficial results from its office are not expected until Wednesday night. Despite the delay, county clerks are still expected to begin reporting out results.

If counties are reporting results and they release lots of absentee/early votes, there could still be a projection tonight out of Michigan. The delay in results is due to a 2018 law that allowed for absentee voting without needing an excuse, resulting in an influx of absentee ballots.

State election officials are now in "uncharted territory" this cycle, Tracy Wimmer, a spokesperson for the secretary of state, told ABC News. Michigan Democrats say a total of 821,124 absentee ballots have been returned to the secretary of state for all voters (across parties), which is a 55% increase from 2016.

"This is a huge shift in workload for the clerks and there's different capacity in every jurisdiction. Our elections are decentralized so trying to execute the counting - the tabulation process - each county is handling it and each clerk is handling it," Wimmer said.

ABC News' Kendall Karson and Meg Cunningham reporting.

6:01 p.m. Trump hits Dems over Green New Deal in play to Michigan voters

With the Democratic Michigan primary in progress, President Trump is arguing on Twitter that Democrats "all want to get rid of cars," in an apparent reference to the Green New Deal, which doesn't actually call for that.

"If you like automobiles, how can you vote for a Democrat who all want to get rid of cars, as quickly as possible, especially if they are powered by gasoline. Remember also, no more than one car per family. I, on the other hand, have new plants being built all over Michigan, Plus!" the president tweeted.

While documents released by Rep. Alexandria Ocasio-Cortez's office prior to the Green New Deal's release called for similar proposals (her office said they weren't final and weren't supposed to be released), the plan itself does not push for these prohibitions.

Read a fact check here.

ABC News' Will Steakin reporting.

5:45 p.m. Interest in return to Obama administration policies varies: Preliminary exit poll results

Interest in a return to the policies of the Obama administration varies widely in tonight's states. In Mississippi, in preliminary results, 61 percent say they'd like to see the next president return to the policies of the Obama administration – the most in any state so far this year for which we have exit poll results. In Washington, this falls to 41 percent, with 44 percent instead saying they'd like to see more liberal policies, according to preliminary exit poll results.

The results also find general dissatisfaction with the country's economic system. Only 4 to 10 percent say it works well enough as is; among the rest, 45 percent or more in Missouri, Washington and among in-person voters in Michigan say the system needs “a complete overhaul,” with the rest calling for minor changes. (The question wasn't asked in Mississippi.)

Because of a sampling problem, today's Michigan exit poll does not include the telephone survey that was conducted to capture the opinions of early and absentee voters there. They account for an estimated 40 percent of voters in the Michigan Democratic primary.

ABC News' Polling Director Gary Langer reporting.

5:38 p.m. Here's a glimpse at the voting breakdown so far among races according to preliminary exit poll results

In terms of race and ethnicity, in contests to date, white voters have split by a close 30-28% between Biden and Sanders, and Hispanics have gone 44-25% for Sanders. (Hispanics are disproportionately young, and Sanders does best with young voters.) Blacks, by contrast, have voted overwhelmingly for Biden, 56-17% according to preliminary exit poll results.

People wait in line to get their ballot to vote in the Michigan primary election at Chrysler Elementary School in Detroit, March 10, 2020.

People wait in line to get their ballot to vote in the Michigan primary election at Chrysler Elementary School in Detroit, March 10, 2020.Jeff Kowalsky/AFP/Getty Images

Blacks have accounted for 15% of Democratic voters in previous contests this year. In preliminary exit poll results tonight, their numbers range from 64% in Mississippi to 18 percent in Michigan (excluding the estimated 40% overall in Michigan who voted early or absentee), 17% in Missouri and 4 percent in Washington. (The share of blacks in Mississippi, preliminarily, is down from 71% in 2016.) Hispanics are less prevalent.

ABC News' Polling Director Gary Langer reporting.

5:37 p.m. Gender turnout among groups is important: Preliminary exit poll results

Turnout among groups is important in these races, with race or ethnicity, ideology, partisanship and age among the key factors.

Another, potentially, is gender: Women have accounted for 57% of voters in previous primaries and caucuses for which we have exit or entrance polls and have supported Biden over Sanders by 35-26%. Men have supported Sanders, more narrowly, 34-30 percent. In preliminary results so far, women account for 52 to 58% of the turnout today.

Because of a sampling problem, Tuesday's Michigan exit poll does not include the telephone survey that was conducted to capture the opinions of early and absentee voters there. They account for an estimated 40 percent of voters in the Michigan Democratic primary.

ABC News' Polling Director Gary Langer reporting.

5:36 p.m. Biden heads to Philadelphia

Vice President Joe Biden will make his way to Philadelphia after canceling his rally in Cleveland. Biden will give his marks from there after tonight's primaries. He is expected to leave Ohio shortly.

ABC News' Molly Nagle reporting.

5:16 p.m. Biden prevails in trust to handle a major crisis in preliminary exit poll results

Former Vice President Joe Biden prevails in trust to handle a major crisis in preliminary exit poll results, leading Bernie Sanders on the question by 34 percentage points among voters today in Missouri, 19 points in Washington state and 19 points, as well, among today's voters in Michigan.

While not necessarily indicating vote preferences, the margins are substantial – 61-27% for Biden over Sanders in trust to handle a major crisis in Missouri, 46-27% in Washington (with 21 percent selecting Elizabeth Warren, who's dropped out of the race), and 51-32% among in-person voters today in Michigan. The question wasn't asked in the fourth state with exit polls today, Mississippi.

The Michigan results require an important caveat: The National Election Pool reports that a sampling problem has prevented it from including telephone survey results – produced to capture the views of early voters – in the Michigan exit poll, as intended. As such the exit poll does not include the views of early voters there, an estimated 40 percent of all voters in the primary there.

The “trust in a crisis” question may be especially relevant given concerns about the spread of the new coronavirus in the United States. Washington state has been an epicenter of the outbreak, and there a vast 82 percent are very or somewhat concerned about it, including 38 percent “very” concerned. Concern is higher among older voters, typically a strong group for Biden.

ABC News' Polling Director Gary Langer reporting.

5:05 p.m. Kansas City Mayor turned away from polls over name entry error

Kansas City Mayor Quinton Lucas was turned away from his polling place this morning after a poll worker entered his name incorrectly in the system.

Lucas posted about the incident on Twitter, saying that the his name "wasn't in the system even though I've voted there for 11 years, including for myself four times! Go figure, but that's okay. We'll be back later today!"

I made a video this morning about the importance of voting and then got turned away because I wasn't in the system even though I've voted there for 11 years, including for myself four times! Go figure, but that's okay. We'll be back later today! #Vote #KCMO pic.twitter.com/3mYNrO6jmC

— Mayor Q (@QuintonLucasKC) March 10, 2020

Shawn Kieffer, the director of the Board of Elections, later told ABC News that the reason Lucas' name didn't come up was because the poll entered his name backwards, as Lucas Quinton, not Quinton Lucas.

The mayor has yet to return to the poll, according to Kieffer.

ABC News' Meg Cunningham reporting.

4:44 p.m. Biden campaign also cancels rally tonight in Cleveland

Former Vice President Joe Biden's campaign is also canceling their rally tonight in Cleveland.

"In accordance with guidance from public officials and out of an abundance of caution, our rally in Cleveland, Ohio tonight is cancelled. We will continue to consult with public health officials and public health guidance and make announcements about future events. In the coming days. Vice President Biden thanks all of his supporters who wanted to be with us in Cleveland this. Additional details on where Vice President Biden will address the press tonight are forthcoming," Communications Director and Deputy Campaign Manager Kate Bedingfield tweeted.

ABC News' Johnny Verhovek reporting.

4:29 p.m. Delay expected in Michigan primary results after new law

Michigan election officials are preparing for a delay in the primary results after there was a surge in absentee ballots sent in this year.

The high volume of absentee ballots comes after "unprecedented shift in the way that people have been voting," according to a spokesperson for the secretary of state.

The state amended its constitution in 2018 to allow for absentee voting without needing an excuse.

Voters cast their ballots in the Democratic primary election in Detroit, March 10, 2020.

Voters cast their ballots in the Democratic primary election in Detroit, March 10, 2020.Rebecca Cook/Reuters

More than 500,000 ballots have already been cast, with the state seeing an 80% increase in applications for absentee ballots this year, compared to 2016, according to the secretary of state's office.

Officials said the new law, not the novel coronavirus, is more likely the reason behind the influx of ballots.

ABC News' Kendall Karson reporting.

4:27 p.m. Sanders campaign cancels Cleveland rally tonight amid public health concerns

Sen. Bernie Sanders, I-Vermont, canceled a rally in Cleveland, Ohio Tuesday night amid the novel coronavirus spread in the U.S. "We are heeding the public warnings from Ohio state officials, who have communicated concern about holding large, indoor events during the coronavirus outbreak," according to a statement from campaign communications director Mike Casca. "Sen. Sanders would like to express his regret to the thousands of Ohioans who had planned to attend the event tonight." Casca said all future Bernie 2020 events will be evaluated on a case by case basis.

There have been at least 808 confirmed cases of COVID-19 in the United States, according to a case count by Johns Hopkins University. At least 28 people have died in the U.S., per ABC News' count.

ABC News' Adam Kelsey reporting.

4:06 p.m. Election officials prepare amid coronavirus spread

As voters in six states head to the polls for Tuesday's primaries and the novel coronavirus continues to spread in the U.S, election officials are closely monitoring the situation as the federal government shifts from a containment strategy into a mitigation phase.

Election workers wear protective face masks as they check voters to get their to vote in the Michigan primary election at Central United Methodist Church in Detroit, March 10, 2020.

Election workers wear protective face masks as they check voters to get their to vote in the Michigan primary election at Central United Methodist Church in Detroit, March 10, 2020.Jeff Kowalsky/AFP/Getty Images

The new coronavirus has complicated the 2020 election season with its unrelenting global impact, killing more than 4,000 people and infecting over 110,000 worldwide.

Some state officials are making adjustments to their primary administration efforts even before confirmed cases of the coronavirus reach their state.

In Idaho, where the state holds a presidential preference vote on Tuesday and a primary in May, state officials have sped up parts of contingency plans that were already in place to address election disruptions. The Idaho secretary of state's office accelerated orders for additional laptops in order to provide increased flexibility for employees to operate remotely or in emergency conditions.

ABC News' Luke Barr and Kelly Cannon reporting

11:03 a.m. Biden spars with auto worker over gun rights

Former Vice President Joe Biden got into a heated exchange with an auto worker while visiting the Fiat-Chrysler Automobile (FCA) assembly plant in Detroit, Michigan, ahead of the primaries.

Democratic presidential candidate Joe Biden looks on as Shannon Watts, Founder of Moms Demand Action speaks during a campaign stop at Driving Park Community Center in Columbus, Ohio, March 10, 2020.

Democratic presidential candidate Joe Biden looks on as Shannon Watts, Founder of Moms Demand Action speaks during a campaign stop at Driving Park Community Center in Columbus, Ohio, March 10, 2020.Mandel Ngan/AFP/Getty Images

Though Biden was greeted warmly by most of the workers, he fired back at one man who claimed he wanted to "take our guns."

"You are actively trying to take away our second amendment," the worker said.

"You're full of s---," Biden replied.

He went on to say that he supports the second amendment, but does not believe anyone needs 100 rounds. Biden eventually told the man not to be such "a horse's a--."