Fire officials are investigating an early morning 2-alarm fire at an abandoned warehouse on Vallejo's Mare Island as suspicious.
At 3:47 a.m., firefighters responded to a report of a fire at a warehouse near J Street and Azuar Drive, fire spokesman Aaron Klauber said.
Witnesses told fire officials they heard an explosion in the area, followed by flames and smoke, according to Klauber.
Upon arrival, firefighters observed smoke and flames coming from the first and second stories of the three-story building.
Firefighters were able to knock down the blaze from the outside and eventually extinguished the fire, Klauber said.
No one was inside the warehouse at the time, however, firefighters found evidence that people may have been living inside the vacant building, according to Klauber.
No injuries were reported and the cause remains under investigation.