HARRISBURG, Pa. — A primary election like none other in state history awaits Pennsylvania voters Tuesday, when those who have not contributed to the flood of mail-in ballots may encounter new machines designed to improve security by creating a verifiable paper record.

Polling places in some counties have been moved or consolidated to cope with a pandemic-driven drop in election volunteers, and special social distancing rules will be in place at the still-open locations.

Twenty-two counties, or about one-third, will use new voting systems for the first time, while this election marks the debut of no-excuse mail-in ballots under a law approved by Gov. Tom Wolf and lawmakers last fall.

More than 1.8 million voters applied for a mail-in or absentee ballot, smashing expectations by state officials. But some officials have said they worried that voters wouldn't receive their ballot in time to return it by the 8 p.m. election day deadline.

Delaware County, which already sent out approximately 80,000 ballots, said it was still sending out 6,000 ballots on Monday, and that another 400 would not be mailed to voters who had requested them due to "timing and staffing constraints."

Voters who do not receive their ballot in the mail can vote provisionally at their polling location. In addition, Delaware County, Philadelphia and some other counties were providing ballot drop-off spots.

In a video conference with reporters on Monday, Secretary of State Kathy Boockvar said state elections officials were monitoring nationwide protests over the police killing of George Floyd in Minneapolis but have not made any changes to voting as a result.

Boockvar said more than a million voters have already cast ballots by mail or by dropping them off at county elections offices.

Boockvar said results in close races may be delayed and urged voters to be patient.

“It’s not going to look or feel as it has in non-pandemic times, and the results may take longer,” she said.

Polls will be open from 7 a.m. to 8 p.m. Tuesday.

The result of the highest profile contests on the ballot are a foregone conclusion, as President Donald Trump and former Vice President Joe Biden are the presumptive major-party nominees.

The only statewide races are for the “row offices” — attorney general, auditor general and treasurer.

Democratic Attorney General Josh Shapiro is unopposed in seeking his party's nomination, as is Pittsburgh lawyer Heather Heidelbaugh for the GOP nod. There is a six-candidate Democratic primary and a lone Republican seeking the nominations for attorney general, as incumbent Eugene DePasquale is term-limited. Unopposed in the treasurer primary are incumbent Democrat Joe Torsella and Republican Stacy Garrity.

All 18 of the state's members of the U.S. House of Representatives are seeking reelection, although only two have primary opposition from within their own party — suburban Philadelphia Rep. Brian Fitzpatrick, a Republican, and Pittsburgh Rep. Mike Doyle, a Democrat.

In the Legislature, all 203 House seats and half the 50-member Senate are up this year. The most notable vacancies were created by the retirements of House Speaker Mike Turzai, R-Allegheny, and Senate President Pro Tempore Joe Scarnati, R-Jefferson.

There are 17 retirements in the state House, which currently has a 110-93 Republican majority, and two in the Senate, where the GOP, with one independent, holds a 29-21 margin.

Primary voters will also pick delegates and alternates for the two major parties’ presidential nominating conventions.

The election was postponed from April 28 because of the COVID-19 pandemic. In the meantime, Pennsylvania voters have returned about 1.1 million ballots by mail of the 1.8 million requested.

Before last fall's state law, those who did not wish to cast their ballots in person had to provide one of a limited number of permitted excuses to qualify for an absentee ballot.

The unexpected volume of mail-in ballot requests has proven to be a challenge for county elections officials, and they are warning that election results are likely to be delayed well past election night. Where those delays will occur and how long it will take to get results are open questions.

The conversion to new machines caused some problems in November, including malfunctions in Northampton County that one official likened to a three-alarm fire.