Some of Pennsylvania's most populous counties are starting to press Gov. Tom Wolf to allow them to conduct the June 2 primary election entirely by mail amid fears that the coronavirus would pose a threat to poll workers and voters.

The top government official in Allegheny County, Pennsylvania's second-most populous, said Monday that holding an in-person election in the midst of the crisis would be a "disaster."

Allegheny County Executive Rich Fitzgerald said he wants Wolf to expand an emergency declaration to allow the county to mail ballots to every registered voter and avoid the legal requirement that it open hundreds of polling places staffed by thousands of poll workers.

"I'm very concerned that we can actually operate this and actually function, getting this many people to work the election and in voting places," Fitzgerald said in an interview.

Officials in a pair of heavily populated suburban Philadelphia counties, Montgomery and Chester, are also backing the idea of an all-mail election, while Philadelphia is making preparations for it in case Wolf orders it.

Asking people to work at polling places and vote there goes against the social-distancing requirements for residents to slow the spread of the virus in Pennsylvania, Fitzgerald said.

Wolf's office said Monday that the governor is evaluating options to increase the percentage of voters who vote by mail, "which he believes will be important."

There are challenges to moving to an all-mail election, including ensuring that voting is accessible to the disabled and that ballots are mailed to the correct addresses, Wolf's office said.

Democrats pressed for a provision in legislation last month to require counties to send mail-in ballot applications to every voter, but it lacked support in the Republican-controlled Legislature and didn't pass.

Lawmakers did, however, delay the primary election from April 28 to June 2.