A Pennsylvania county official warned Wednesday that potentially thousands of ballots mailed to voters have gone missing, with officials now rushing to send out new ones.

Leslie Osche, chair of the Butler County board of commissioners, told local CBS affiliate KDKA that officials have mailed new ballots, overnighted ballots to people residing out of state such as college students, and even had sheriff’s deputies hand-deliver ballots.

Osche said it was unclear how many ballots have apparently gone missing, but estimated — based on the number of calls and emails that have flooded local offices — that it could well be in the thousands.

“At first we thought that maybe it just was a delay in the postal system,” Osche told the outlet. “And that could still be the case. But nonetheless, when we realized that, we changed our strategy and now have begun to tell folks that if they haven’t received a ballot, they still have multiple options.”

The U.S. Postal Service said in a statement Wednesday reported by local media that the post office is “unaware of any significant delays or issues and is in regular contact with the Board of Election as we work to locate and deliver ballots as they are presented to us.”

The Pennsylvania Department of State has asked the Postal Service and the county to investigate the apparently lost ballots, Spotlight PA reported. Of the nearly 40,000 registered voters in Butler, only a quarter of them appeared to have returned their ballots, the outlet reported. That would make it the lowest return rate by far in any Pennsylvania county.

Butler County voters still have a few options left in casting their ballots. They can go to the Bureau of Elections to collect and submit their ballots or go to their local polling place to vote in person.

Pennsylvania is a key battleground state for President Trump and his reelection campaign – having made multiple trips to the area in the weeks leading to Election Day.