The blaze was reported around 10:30 a.m. at the Muirwood Apartments complex at 600 Center Ave., a Martinez police lieutenant said.
The fire appears to have started in an upstairs unit of a building in the back of the sprawling complex.
Lynn Wheeler, who lives next door to one of the apartments destroyed by the blaze, said her neighbor told her she had gone out to her balcony to smoke a cigarette and had come back to find her bed on fire.
Another neighbor, 49-year-old Glenda Ramero, said she saw flames shooting from an upstairs apartment balcony and heard glass shattering as the unit's windows broke.
Ramero said she quickly got her wheelchair-bound mother and 8-year-old daughter out of her apartment.
As of 11:45 a.m., the blaze had been extinguished. Firefighters remained at the scene mopping up.