SEATTLE (AP) — Authorities were investigating Monday after early morning fires were set at ballot boxes in Portland, Oregon, and in nearby Vancouver, Washington, where hundreds of ballots were destroyed.

The Portland Police Bureau reported that officers and firefighters responded to a fire at a ballot box at approximately 3:30 a.m. and determined that an incendiary device had been placed inside. Multnomah County Elections Director Tim Scott said a fire extinguisher in the mailbox protected almost all of the ballots; only three were damaged, and his office planned to contact those voters to help them obtain replacement ballots.

A few hours later, television crews across the Columbia River in Vancouver captured footage of smoke pouring from a ballot box at a transit center. Vancouver is the largest city in Washington’s 3rd Congressional District, the site of what is expected to be one of the closest U.S. House races in the country, between first-term Democratic Rep. Marie Gluesenkamp Perez and Republican challenger Joe Kent.

Clark County Auditor Greg Kimsey in Vancouver told The Associated Press that the Fisher’s Landing Transit Center ballot box also had a fire suppression system, but for some reason it was ineffective. Respondents removed a burning stack of ballots from the box and Kimsey said hundreds were lost.

“Heartbreaking,” Kimsey said. “It is a direct attack on democracy.”

There were surveillance cameras covering the mailbox and its surrounding area, he said.

The last round of voting at the transit center drop box was at 11 a.m. Saturday, Kimsey said. Anyone who dropped their ballot after that was urged to contact the accounting office to obtain a new ballot.

The office will increase the frequency of ballot collections, Kimsey said, and change collection times to the evening, to avoid filling the ballot boxes with ballots overnight when it is considered more likely similar crimes will occur.

On October 8, an incendiary device was also found on or near a ballot box in downtown Vancouver. It did not damage the box or destroy any ballots, police said. The FBI and other agencies had investigated.

Washington and Oregon are both voting-by-mail states. Registered voters receive their ballots in the mail a few weeks before the election and then return them by mail or by placing them in ballot boxes.

Last week, officials in Phoenix said about five ballots were destroyed and others damaged when a fire was set in a mailbox at a US Postal Service station there.

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Christina A. Cassidy of Atlanta contributed.