Firefighters are battling a growing brush fire at the Camp Pendleton Marine Corps base in Southern California.

The uncontained fire had consumed 75 acres near San Mateo Canyon late Thursday, base fire inspector Bill Gick says.

The blaze was started accidentally in the afternoon by troops training at the base's northern end, Gick says.

Two helicopters and three planes dropped water on the flames before nightfall.

No structures are threatened. Firefighters plan to work through the night, Gick says.