Firefighters responded to a report of a fire at the Bayshore Villa Trailer Park at 3499 E. Bayshore Road around 1:45 a.m., San Mateo County sheriff's Lt. Ray Lunny said.
Residents of a trailer near where the fire was burning extinguished the flames with a garden hose before the firefighters arrived, Lunny said.
Investigators later discovered that other unoccupied homes at the trailer park had been soaked with a flammable liquid, Lunny said.
Anyone with information on the fire is asked to call San Mateo County sheriff's Detective Saul Lopez at (650) 363-4347. Callers who wish to remain anonymous may contact the sheriff's tip line at (800) 547-2700.