KITTERY, Maine — The five-alarm fire that caused about $400 million in damage aboard a nuclear submarine appears to have started in a vacuum cleaner, the Portsmouth Naval Shipyard said in a statement.

Meanwhile, the same vessel — the USS Miami — was evacuated Wednesday morning as a precaution after a fire alarm sounded. Officials blamed the mishap on a faulty alarm.

Three teams of investigators are looking into the cause of the fire, which began the evening of May 23. Firefighters from four states responded to aid the ship’s crew and shipyard firefighters.

“Preliminary findings indicate the fire started in a vacuum cleaner used to clean worksites at end of shift, and stored in an unoccupied space,” a shipyard news release stated.

It took about 10 hours to extinguish the blaze.

Specifics about the cause and a damage assessment are still being compiled. An initial report containing conclusions and recommendations is expected in the next two weeks, according to the news release.

The Los Angeles-class attack submarine has been undergoing repairs in dry dock since March 1.

Shipyard firefighters responded to an alarm Wednesday at 8:55 a.m. Non-essential personnel were evacuated from the submarine, and firefighters did not detect any fire, smoke or injuries, according to Deb White, shipyard spokesman.

“It looks like a faulty alarm,” White said, adding firefighters will determine what caused the alarm to sound.

Last week, members of the shipyard’s workforce returned to the submarine to help clean up after the fire, do damage assessment and continue the original repairs.

“Since that time, the first phase of the cleanup process, which included de-watering the ship and installation of temporary services (i.e. lighting, staging, etc.), has been completed. For the next phase, detailed cleaning, the Navy is pursuing contracted cleaning services which are expected to be awarded later this week,” the release stated.

Navy personnel estimated the “initial rough repair cost” will be about $400 million. That does not include an additional 10 percent for secondary effects, “such as disruption to other planned work across all Naval shipyards and the potential need to contract work to the private sector,” the news release said.

“This estimate was developed so that funding can be identified to support the repairs, which would be accomplished at Portsmouth Naval Shipyard. This estimate will be refined as more data is gathered and testing completed,” the release said.

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John Quinn may be reached at jquinn@newstote.com.