PHOENIX (AP) — Arizona opened election polls Tuesday for Democrats to pick a presidential candidate as the state deals with a public health crisis that has crippled parts of the nation— and as the number of returned mail-in ballots has already surpassed 2016.

The state's top election official declined to seek a delay because of the coronavirus, saying Monday that there was no certainty that putting off voting would help.

“We have no guarantee that there will be a safer time to hold this election in the future,” Secretary of State Katie Hobbs said during a news conference in Phoenix alongside Republican Gov. Doug Ducey and other state officials.

Hobbs said after the public votes, an army of election workers will have to process ballots in warehouses, an undertaking that could get more dangerous as time passes.

The Democratic ballot has 18 names, but the race boils down to a face-off between Vermont Sen. Bernie Sanders and former Vice President Joe Biden. More than a dozen other candidates dropped out, but they still appear on the ballot.

Polls opened at 6 a.m. and close at 7 p.m.

The vast majority of the 1.2 million registered Arizona Democrats cast ballots early by mail, but about 300,000 can vote in person Tuesday. According to figures obtained by The Associated Press, turnout among Democrats has already surpassed the 2016 election. Over 480,000 votes had been cast by Tuesday morning.

At a polling place at a Lutheran church in Phoenix, a steady stream of voters arrived during an hour's span Tuesday morning. At times, several had to wait at the door before being allowed to enter after other voters left the building.

Ben Halloran, a candidate for a Maricopa County constable position, was collecting signatures from fellow Democrats on nominating petitions at a table with disinfectant wipes and spray to clean the table and the pens voters used to sign his petitions.

“Ï think we have a valid concern for health," said Halleran, wearing medical gloves and not shaking hands.

Melissa Cox, 42, dropped off her absentee ballot at an empty emergency polling place in South Phoenix on Monday. She said she's concerned about the coronavirus outbreak but was mainly trying to avoid potential lines and crowds on Tuesday.

“I'm trying to not be panicked,” said Cox, an admissions counselor for a vocational school who voted for Biden.

Around the state Monday, election officials consolidated polling places, lined up backup poll workers and opened emergency voting centers where people can cast a ballot early as parts of the state shut down to avoid spreading the new virus. Hours for absentee drop boxes were also extended.

Ducey, a Republican, and Hobbs, a Democrat, released a video Monday outlining the precautions being taken at polling places. They include measures to keep distance between people, frequent hand washing by poll workers and regular disinfecting of equipment. Officials also asked voters to wash hands before and after visiting the polls.

“It's been a lot of work, but it's well worth it because our democracy is worth it,” Hobbs says in the video.

Hobbs on Friday joined the top election officials in the three other states holding primaries Tuesday in pledging to press forward, even as two states scheduled to vote in the coming weeks — Louisiana and Georgia — delayed their primaries. Delaying Arizona's primary would require an act of the Legislature.

Ohio's governor, Mike DeWine, changed his mind Monday and asked a judge to delay voting. That request was rejected, but the state's top health official postponed them over public safety concerns.

Voters in Florida and Illinois are voting Tuesday.

Maricopa County officials scrambled to consolidate from 229 to 151 polling places as nursing homes and churches backed out of serving as locations. The remaining polling places are “vote anywhere centers” that allow any registered Democrats in the state's most populous county to cast a ballot. The locations are available online at http://Maricopa.Vote.

The COVID-19 disease caused by the virus for most people causes only mild or moderate symptoms. For some, particularly older people or those with underlying health conditions, it can cause more severe illness.

Sanders and Biden will vie for the 67 possible delegates to the Democratic Convention in Milwaukee in July. The state party will award delegates to them in proportion to the number of votes they receive. Votes cast for the remaining candidates will earn them delegates if they get at least 15% of the vote. Dropped-out candidates can direct their delegates to back their favored candidate, but they’re free to back who they want.

Republicans aren't holding a primary for incumbent President Donald Trump. Libertarians chose delegates to their convention at a state party meeting.

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Associated Press photographer Matt York and AP writer Paul Davenport contributed.