The USS Midway, an aircraft carrier-turned-museum, was evacuated due to a fire caused by a welder early Wednesday.

San Diego fire department spokesman Lee Swanson said shortly before 7 a.m. (10 a.m. ET) that firefighters found smoke two levels below the flight deck where crews were working overnight, according to CNN.

"We have ... not located (a) fire," Swanson added, adding that crews noticed excessive heat. "We have most of our units staged and available. And we are working with the museum and volunteers to get access to find the source."

Midway spokesman Scott McGaugh revealed that firefighters later found the blaze in a steel compartment closed to the public, and that the fire caused minimal damage, according to ABC News.

San Diego Harbor Police stated that all employees aboard at the time were evacuated, and both entrances were blocked off, ABC's San Diego affiliate ABC 15 reported. The process was quick since most employees were arriving to work when the incident took place.

Since the fire was minor and it happened early in the day, the museum opened at 10 a.m. (1 p.m. ET) on Wednesday as usual.

The Midway was commissioned a week after World War II ended. It was used throughout the Vietnam War and was decommissioned after service in Operation Desert Storm.

The aircraft carrier now operates as a non-profit museum run by a board of directors.