Election results from Milwaukee will likely be delayed until well after midnight as election officials there are recounting 30,000 absentee ballots due to a “sealing” error with tabulation machines.

A spokesman for Milwaukee, Jeff Fleming, says the recount is being conducted “out of an abundance of caution.”

“We have no reason to believe that there was any compromise to any of the machines,” he told the Milwaukee Journal Sentinel. However, he said human error was to blame for doors on the tabulation machines not being “sealed.”

The error was discovered in a polling station at downtown Milwaukee. 

A spokeswoman for the Milwaukee Election Commission, Caroline Reinwald, said the tabulation machine doors were not properly closed.

Republican and Democratic observers who examined the machines did not raise concerns about their integrity. The chairman of the Republican Party of Milwaukee County, Hilario Deleon, told CBS 58, “I didn’t really see anything nefarious. It was just probably human error at this point in time.”

Officials in Wisconsin, where absentee ballots cannot be processed and counted until Election Day, previously predicted the results in the state would be known after midnight. However, the recount could add several hours to the tabulation process. 

While election officials insisted there was no reason to believe the machines were tampered with, the Republican National Committee criticized Milwaukee officials.

The chairman of the RNC, Michael Whatley, and co-chair, Lara Trump, said in a statement, “Throughout the day we have been monitoring slow ballot counting in Milwaukee. Now, our legal team has learned that the counting took place in insecure conditions, and the city now has to start over, wildly extending the counting timeline.”

“This is an unacceptable example of incompetent election administration in a key swing state: voters deserve better, and we are unambiguously calling on Milwaukee’s officials to do their jobs and count ballots quickly and effectively. Anything less undermines voter confidence,” the statement added.

Wisconsin is one of the seven key battleground states that could determine the results of the presidential election. A delay in the results in the state could prolong the time it takes to determine who won the election.