Firefighters responded to a report of a structure fire at 26350 Carmel Rancho Blvd. at 11:40 a.m.
Employees told firefighters that they had heard an explosion in the basement of the building, Monterey County Sheriff's Cmdr. Chuck Monarque said. The explosions were followed by smoke that inundated the building's inside ventilation system, he said. Investigators found evidence of a flammable liquid in the utility room, officials said.
Employees in the nine units evacuated the building. There was a moderate amount of smoke damage to the building, he said. No injuries were reported.
It may take a few days for the arson task force to find the cause of the fire.
The electricity and phones were down through Tuesday as a result of the fire. An initial damage estimate is roughly $250,000, he said.
This is the second time in three months that the building has caught fire. In June someone had thrown an explosive device with an accelerant.
"It is rare to have two fires at the same building," said Curt Itson, a battalion chief with the California Department of Forestry who is also investigating the fire.