The investigation continues in to what caused an overnight fire Jan. 4 at the West Concord Fire Station.

Fire Chief Mark Cotreau said the blaze likely started inside Engine 4, which was parked inside Station 2 during the fire.

Engine 4 was towed away to an unknown location, where investigators will comb through it for clues to a cause.

Three firefighters - Lieutenant Brad Ferrie and firefighters Bill Haugh and Kevin Fagerquist - were asleep at 12:48 a.m. when the fire broke out, and all made it out safety.

Cotreau said Engine 4 suffered significant damage, and if it needs to be replaced, the cost could be upward of a half-million dollars.

The West Concord ambulance and Engine 8, both stationed in West Concord, will be returned to service after they are cleaned.

Cotreau said firefighters awakened to smoke alarms going off at approximately 12:48 a.m., and called in the fire to the main station on Walden Street.

"We're fortunate, blessed there were no injuries or deaths," Cotreau said.

According to Cotreau, the West Concord station could be closed for up to a week, and firefighters that work out of that station will be housed in space at the Concord Municipal Light Plant.

The fire is similar to one in Acton in 2015. In that incident, a ladder truck caught fire in a fire station bay. According to Cotreau, there is no reason to believe the incidents are related because Engine 4 and the Acton ladder truck had different manufacturers.

Follow Henry Schwan on Twitter @henrycojo.