The four states scheduled to hold primary elections in the United States on Tuesday are promising that the votes will go on despite increasing calls for them to be postponed or delayed because of the coronavirus pandemic.

The governors' offices of Florida, Illinois, and Ohio said on Monday that they are pushing forward with the voting even as some county elections officials conceded that some poll workers - many of them elderly or retired people - are dropping out for fear of catching the Covid-19 disease associated with the coronavirus.

Arizona, also scheduled to vote Tuesday, is expected to proceed as well. So far, two states - Georgia and Louisiana - have said they will postpone their primary elections.

Georgians were scheduled to vote on March 24 and voters in Louisiana on April 4.

The states will now vote in May and June.

Even the candidates themselves have questioned the wisdom of going through with the elections.

In an interview with CNN following Sunday night's debate, Democratic presidential candidate Bernie Sanders said he would hope the governors would listen to health experts about the dangers of mingling with others in public spaces.

"I'm thinking about some of the elderly people who are sitting behind the desks, registering people, doing all that stuff," he said.

"Does that make a lot of sense? Not sure that it does."

The coronavirus outbreak has dramatically upended normal presidential campaign routines, forcing both remaining Democratic presidential candidates off the road.

Both Sanders and frontrunner Joe Biden plan to hold "virtual" campaign events on Monday in an effort to reach voters.

Biden will hold a tele-town hall meeting with voters in all four states on Monday, his campaign said, while Sanders planned a "digital rally" livestreamed broadcast featuring musician Neil Young and actress Daryl Hannah.

State officials said they were taking extra precautions to protect the public on Tuesday.

In Florida, polling places located in nursing homes and assisted living facilities have been moved to avoid exposing the residents to outsiders. Florida's Broward County is stocking its 421 polling locations with extra supplies, including 4 000 rolls of paper towels, gloves and more than 400 bars of soap.

"We've purchased gallons of rubbing alcohol and are having them transferred to spray bottles," said spokesperson Steve Vancore.

"We've ordered cases upon case of Clorox wipes so poll workers can frequently wipe down the equipment and wipe down the voting booths."

Broward, which is home to Fort Lauderdale and the state's second-largest county, relies on 3 800 paid polling workers. But the county has recruited 4 500, Vancore said.

"We have extra, and so far, so good," he said, noting very few are calling out due to virus concerns. The Democrats' presidential nomination fight has been relegated to an afterthought as the US grapples with a health crisis likely to grow exponentially in the coming weeks. If the primaries are held as scheduled, the vote Tuesday could spell a death knell for Sanders, who cannot afford a repeat of last week's performance, when he lost four of the six states to Biden.

Sanders also appears likely to lose in Washington state, where the votes are still being counted. Florida, with 219 of the 1 991 delegates needed to secure the nomination, is the big prize of the day, but Sanders has struggled in that state with both seniors and some older Latinos, who may harbour ill will toward anyone associated with socialism because of experiences in places such as Venezuela and Cuba. A bad night in Florida could make Sanders's path to the nomination all but impossible.