Voters in Florida, Illinois and Arizona cast ballots in Democratic primaries Tuesday in the face of a rapidly spreading coronavirus pandemic that has cast a pall over the US presidential nomination race between Joe Biden and Bernie Sanders.
A fourth primary state, Ohio, postponed its elections until June on orders of Republican Governor Mike DeWine, who told voter to stay at home amid the escalating public health emergency.
The US has officially registered more than 5 600 coronavirus cases, although that is believed to be a fraction of the real number, which has been depressed by the failure to roll out testing.
Election authorities are braced for disruptions with President Donald Trump's administration urging people to avoid gatherings of more than 10 people.
Trump backed the Ohio delay at a White House news conference, telling reporters asking what he was doing to protect elections: "What I am doing is getting rid of the virus. That's the only thing we can do."
In Florida, the largest and most populous state voting on Tuesday, some two million people had already voted early or by mail, and turnout was expected to be exceptionally low.
Adding to the obstacles, state authorities had to move dozens of precincts from senior centers to protect against the virus.
Gabriela Carrilho, a 51-year-old who works in marketing, donned gloves before casting her ballot at a nearly deserted elementary school in Miami Beach.
"I think if you don't participate, then things never change," she said.
She and others said they felt safe voting.
"There was hand sanitiser at every single station," said 29-year-old Matt Don. "They kept a safe distance from me. Everybody in there is keeping safe."
In Illinois, Chicago election commissioners were scrambling to find judges after about 850 informed the county clerk's office they wouldn't show up, the Chicago Tribune reported.
Arizona polls opened a few hours after those in Florida and Illinois, with voters trickling in to cast ballots.
Democrats are in the midst of choosing a nominee who will challenge the Republican incumbent in November's election, but doubts and concerns have undercut the process.
"While Arizona, Florida and Illinois are still voting today, going to the polls amid the coronavirus outbreak is a personal decision and we respect whichever choice voters make," Sanders said in a tweet.
Despite DeWine's move to shutter polling stations in Ohio, he appeared to be a lone official voice calling for delay, while Trump has said it is "up to the states" to make the call.
But the vote could be undermined in part by a potential scare factor for the elderly, who are at highest risk of contracting COVID-19.
Officials in Florida, with the most delegates in play Tuesday, said the state is pulling out all the stops to keep the process safe.
In Arizona, Governor Doug Ducey said state and Democratic Party officials agreed that the primary should go on.
"We have no guarantee that there will be a time in the future when it will be safer than tomorrow," Ducey said Monday.
Biden, 77, tops polling by significant margins in Arizona, Illinois and especially Florida, where the former vice president could strike a hammer blow against his rival by building an insurmountable lead in the delegate count.
Tuesday may be a make-or-break moment for the leftist Sanders, who will face mounting pressure to quit if he does not score a major upset.
Meanwhile, Americans are staying home from work or school by the millions as the country implements emergency measures against a worsening crisis.
Kentucky on Monday announced a delay in its primary from May until June, while Georgia, which was next in line to vote on March 24, is delaying until May.
Louisiana had earlier postponed its April election to June 20.
Biden and Sanders say they will campaign exclusively online for now -- a scenario unheard of at the height of a US presidential primary battle.
Both are taking precautions during the outbreak: they are washing hands frequently, staff is working from home, and live campaign events have been scrapped.
Sanders hosted a "digital rally" Monday night featuring high-profile supporter and veteran rocker Neil Young.
The inability to campaign in person imposes a particular handicap on Sanders, who has consistently mobilized large and enthusiastic crowds at his events.
Sanders has acknowledged he is now the underdog in the delegate race but stressed his progressive movement has "transformed" the 2020 campaign.