Heath officials in Ohio have postponed the state’s primary vote just hours before polls were set to open, an 11th-hour decision that came after a judge denied the governor’s request to postpone the vote because of the coronavirus.

The health director, Amy Acton, declared a health emergency that would prevent the polls from opening out of fear of exposing voters and volunteer poll workers, many of them elderly.

Arizona, Florida and Illinois were proceeding with their presidential primaries.

Earlier on Monday, Ohio’s Governor Mike DeWine recommended that his state postpone in-person voting during Tuesday’s primary elections. DeWine said he alone did not have the authority to postpone the election, but lawyers would file a lawsuit to try to move the in-person voting date to 2 June.

“We cannot conduct this election tomorrow,” DeWine said, adding that Ohioans should not be forced to make the “choice between their health and their constitutional rights and their duties as [an] American citizen”.

Later on Monday, in an interview with CNN, DeWine said without drastic moves tens of thousands of poll workers, many of them “over the age of 65” would be in places where the virus could spread.

“We in Ohio have to take very tough actions and I know people in Ohio today are very upset, I respect that,” DeWine added.

But a Franklin county court of common pleas judge declined to order the postponement on Monday evening. According to a NBC news affiliate, Judge Richard Frye said he was reluctant to override the election date set by the Ohio legislature and that coronavirus has been an issue of concern since January.

The attempted move by Ohio’s governor was the latest example of elected American officials in executive positions taking extra steps to fight the pandemic. The White House on Monday announced new guidelines in an attempt to curb the spread of the virus. In a press conference announcing the new guidelines Trump said he thought postponing elections was “unnecessary”.

Four states were set to hold primary elections on Tuesday as the Democratic frontrunner, Joe Biden, faces off against rival Bernie Sanders for the presidential nomination. In-person votes were still set to take place in Arizona, Illinois, and Florida, despite all facing pressure to stop mass gatherings or activities that could spread the virus.

Georgia already postponed next week’s primary and Louisiana has postponed its scheduled 4 April primary. Kentucky announced on Monday it would postpone its primary from 19 May to 23 June. “My hope is that this delay will allow us to have a normal election,” the secretary of state, Michael Adams, said in a video message.

Last week Ohio officials relocated 160 polling sites that originally were located in senior living facilities. In Illinois on Monday, Governor JB Pritzker ordered that events with gatherings larger than 50 people be canceled. The Illinois department of public health also offered guidance for both poll workers and voters participating in the election on Tuesday, which includes practicing social distancing and “cleaning of visibly dirty surfaces followed by disinfection”.

Tammy Patrick, a former Arizona election official and a senior adviser at the bipartisan Democracy Fund, noted that many poll workers and election officials are elderly, the demographic that makes them particularly vulnerable to contracting the coronavirus. It’s unclear what impact the election changes or the virus itself will have on election officials.

“We don’t know yet what impact this will have on not only the amount of poll workers we have,” Patrick said. “ But the amount of election officials that do this work … they also have the ability to get sick – secretaries of state, all the state election boards, local boards.”

Florida’s governor, Ron DeSantis, vowed again on Monday that the state’s primary would go ahead.

But veteran Democratic pollsters said the pandemic and varying state responses could dramatically change turnout.

“The real answer is we have no idea [what will happen] unfortunately,” said Democratic pollster Pete Brodnitz. “I mean it’s just not one unprecedented thing, it’s an unprecedented thing combined with an unusual thing.”

The two remaining serious campaigns in the Democratic primary – former vice-president Biden’s and Vermont senator Sanders’– have drastically recalibrated their campaign schedules to give virtual town hall and tele-town hall events, to try to continue campaigning while preventing mass gatherings of people.

The voting precautions come at a time when the Sanders campaign needs high turnout among young voters who generally favor him to help reverse the momentum back in his direction. Biden needs older Democratic voters to come out in droves to further fuel his lead in the primary.

“I mean we have the Sanders campaign which is pretty obviously in a downward direction,” Brodnitz said. “Which means his supporters have to take that into account when they’re ready to vote. And it’s harder to motivate people under those conditions. And then you have the coronavirus which is going to be a particular concern to older voters.”

Cornell Belcher, another Democratic pollster, said all the unusual factors going into the elections on Tuesday meant that this “is really uncharted waters”.

“I don’t know what turnout’s going to look like when you have such uncertainty and fear out there,” Belcher said.

Belcher added that it wasn’t clear who had the advantage going into the primaries but he said it was arguable that “Biden clearly has a broader coalition of voters. Does Biden have a stronger core base of voters than Sanders? I don’t know if he does.

“So the question will come ‘does the broadness of Biden’s support enough to overcome what I think is clearly a base energy advantage that Sanders has,” Belcher said.