Six people were displaced late Monday when fire damaged a two-unit apartment building on Mt. Vernon Avenue in Augusta.

Augusta fire Chief Dave Groder said Tuesday that the fire originated on the first floor of the older wood-frame building. Most of the damage was in the first floor apartment. The other apartment is on the second floor.

“There’s significant damage,” Groder said.

No one was injured in the fire, according to Groder.

“All people got out,” he said. “They still have one missing cat.”

The Office of State Fire Marshal is helping his department determine the cause of the fire, which resulted in the building being uninhabitable.

“It’s not considered an intentional act,” Groder said. “It was accidental. We just don’t know why.”

A family of four lived upstairs. They were able to stay with relatives who live next door Monday night, he said. The Red Cross was helping the two people who lived downstairs and lost everything in the fire.

Groder said he is not sure if the building is insured.

About 30 firefighters from Augusta, Chelsea, Vassalboro, Gardiner and Winthrop responded to the scene and the Hallowell and Manchester fire departments covered the Augusta fire station, Groder said. The Augusta Police Department and Central Maine Power Co. also were on scene.

Officials closed down Mt. Vernon Avenue for about two hours, Groder said.

Firefighters left the scene around 12:30 a.m. Tuesday, he said.

Augusta property records show the building was built in 1928.