When Kara Rahn, director of Chester County's Department of Voter Services, left her office Monday night, about 1,400 online voter registration applications were pending.
By the next morning, the number had more than doubled.
Similar scenes played out statewide Tuesday, the last day to register to vote in a state whose 20 electoral votes could be critical in determining the next president.
More than 300,000 voter registration applications were filed online in the last three weeks, according to the Pennsylvania Department of State. On Monday, an average of 3,200 landed each hour - and the 77,400 for the day marked a record since the state began letting voters register online in August 2015. By midday Tuesday, an additional 23,000 applications were filed.
"It's been crazy," State Department spokeswoman Wanda Murren said.
Voters also filed paper application forms and registered through the Pennsylvania Department of Transportation, so final figures - and whom they might benefit - won't be clear until the end of the month.
The surge should come as no surprise. Groups from local party organizations on up to the presidential campaigns held hundreds of registration drives, and efforts intensified over the weekend.
Both major-party presidential nominees have targeted Pennsylvania with visits - with Democrat Hillary Clinton zeroing in on Philadelphia and its suburbs, and Republican Donald Trump focused on the state's conservative center. When they couldn't appear in person, they flew in high-profile surrogates, from running mates to movie stars.
The result has been a crush of new registrations and applications from voters seeking to switch their political affiliation or update their personal information, as well as calls from voters who want to ensure their registration is valid.
The latest registration figures available Tuesday showed Democrats still held a nearly one-million-voter edge over Republicans. But Democrats have lost 109,177 voters since November 2012, and the GOP has picked up 122,979.
In the counties that ring Philadelphia - which by virtue of their density could decide who wins Pennsylvania - Republicans have outpaced Democrats in voter gains in Bucks County, but Democrats have scored significant gains in voter-rich Montgomery and Delaware Counties, and made inroads in Republican-leaning Chester County.
In Philadelphia, where Democrats outnumber Republicans by nearly 8-1, the election focus is on signing up new voters and energizing them to turn out Nov. 8.
Between Monday and early Tuesday afternoon, Philadelphia's elections office was flooded with 25,000 to 30,000 registration forms, according to Tim Dowling, chief deputy to City Commissioner Lisa Deeley. That included 13 packed boxes, holding an estimated 13,000 to 17,000 applications, dropped off by a single person.
"They're coming in hot and heavy," Dowling said. Some applications might have been filled out weeks ago, he said, but many appeared to have been completed more recently. Since April 27, when voter registration reopened after the last primary, the city has received about 200,000 new voter registration paper applications, with about 72,000 in the last three weeks.
Montgomery County logged 16,468 new voters since the primary, according to county election officials. And in Bucks County, 16,171 new voters had registered as of Friday, said Deena Dean, director of the county Board of Elections. About 3,000 landed in October.
"We've been working seven days a week, I'm not even sure for how long," Dean said.
The opposite side of the state was generating a similar status report. "I've never seen anything quite like this," Butler County Elections Bureau director Shari Brewer said.
Her staff arrived Tuesday morning to find 1,900 electronic voter registration applications, nearly five times the previous daily record of about 400.
Fayette County Elections Bureau director Larry Blosser said many voters there waited until the last minute to turn in registration applications, creating "a major headache for us."
Allegheny County has also seen an uptick. Since last November, the voter rolls there increased by about 50,000, said county Elections Division manager Mark Wolosik.
Staff writers Michaelle Bond, Laura McCrystal, Justine McDaniel, and Tricia L. Nadolny contributed to this article, as did Karen Langley of the Pittsburgh Post-Gazette.