WASHINGTON — The new coronavirus hampered efforts by voters to get to the polls in some states on Tuesday as the global pandemic left the Democratic presidential primary consumed with uncertainty.

Leaders in Ohio called off their primary just hours before polls were set to open, citing the need to combat the coronavirus. Voting moved forward in Florida, Illinois and Arizona, but challenges emerged as some poll workers didn›t show up and those who did tried to create distance among voters to comply with new health guidelines limiting large gatherings.

In Florida, the Palm Beach County elections department said many workers failed to show up in at least five locations. The county had 800 volunteers back out as of Monday, with just 100 new volunteers offering to take their place.

No other major problems were reported in Florida, but a coalition of voting-rights advocacy groups filed a lawsuit seeking to extend mail voting in the state’s primary by 10 days.

In Illinois, there was a scramble to relocate about 50 Chicago-area polling places after locations canceled at the last minute and said they would not be available for use on Tuesday. Timna Axel, director of communications for the Chicago Lawyers’ Committee for Civil Rights, said voters have been calling the group’s hotline all morning to get help finding their polling places.

The steady flow of calls — including from some polling place workers — is “unusual for a primary,” Axel said.

Meanwhile, Cook County, Illinois Clerk Karen A. Yarbrough encouraged poll workers to mark space on the floor at polling sites to keep voters a safe distance apart and avoid spreading the virus. She tweeted a photo of a roll of blue tape, a piece of string and a tape measure along with a note that read: “THIS PICTURE CAN SAVE LIVES.”

Not since New York City postponed its mayoral primary on the day of the Sept. 11, 2001, attacks has an election been disrupted in such a high-profile, far-reaching way. That was especially true in Ohio, where Gov. Mike DeWine initially asked a court to delay the vote. When a judge refused to do so, the state’s health director declared a health emergency that prevented the polls from opening.

The decision was a reminder that the most elemental act of American democracy — voting — will be severely tested Tuesday as several states hold presidential primaries while also confronting the impact of a global pandemic. The contests are playing out as the virus’ impact is becoming more tangible with schools closing across the country, workers staying home and restaurants and bars shuttering.

The U.S. stock market on Monday plunged to its worst day in more than three decades.

In the runup to the election, campaigns spent Monday sifting through data and talking to contacts on the ground to assess the impact of the coronavirus on turnout. Former Vice President Joe Biden is moving closer to securing the Democratic presidential nomination but could face a setback if the older voters who tend to support him don›t show up. Vermont Sen. Bernie Sanders, meanwhile, can’t afford to lose support from young voters who have been his most loyal supporters.

The tumult has left the campaign in a state of suspended animation. In-person rallies have been replaced with sometimes-awkward virtual events.

Sanders, the last Democrat standing between Biden and the nomination, isn’t planning to drop out. His campaign looked to have nowhere to go after a big loss last week in Michigan, and another blow landed Monday night when Biden was declared the winner of the primary in Washington state, giving him victories in five out of six states that voted March 10. Yet Sanders’ top advisers see no downside to staying in the race as they assess how the coming days and weeks unfold.

“I don’t have to tell anybody that we are living in a very unprecedented and strange moment in the history of our country,” Sanders said during a virtual rally on Monday, urging supporters that it may be time to “rethink our value system, rethink many of the systems we operate under.”

Still, Sanders faces an increasingly tough path to the nomination. About half of the delegates in the Democratic primary have already been awarded and, if Biden has another big night Tuesday, he will pad an already large and perhaps insurmountable lead. Sanders trails Biden by more than 150 delegates nationally, meaning he›d need to win more than 57% of those yet to be allocated to clinch the Democratic nomination.

Biden’s campaign is trying not to look presumptuous about its prospects at this sensitive moment. Still, the former vice president is making moves to rally more voters to his campaign, including his announcement during the debate that he would choose a woman as a running mate.

Biden appeared to keep his focus Monday on winning the nomination, as he encouraged voters in a telephone town hall to participate in Tuesday primaries but to do so safely.

Joining him was former Surgeon General Dr. Vivek Murthy, who served during President Barack Obama’s second term. Murthy encouraged voters at high risk of contracting coronavirus to vote by mail or use curbside voting, if available, but he also explained precautions elections officials are planning in the Tuesday primary states.

The coming weeks will present additional uncertainties. After Tuesday, the campaign had been set to shift to Georgia next week, but officials there have already postponed their Democratic primary until May 19. That means voting isn’t scheduled again anywhere until March 29 in Puerto Rico — and island officials are also seeking a delay.

The first week in April, meanwhile, would have featured Louisiana, but its decision to delay the primary until June 20 leaves only primaries in far-flung Alaska and Hawaii and caucuses in Wyoming through April 4.

Voting rights groups have advocated for upcoming elections to be postponed, or for states holding them as scheduled to adopt more lenient vote-by-mail and absentee ballot rules so that people don’t have to choose between showing up at a polling place and putting their health at risk.

But Mustafa Tameez, a Democratic strategist with ties to many of the party’s top donors, noted that Americans voted during World War I and World War II.

“There should be no circumstance in which we say, because of a crisis — regardless of the crisis — that we stop our electoral government,” Tameez said.