Firefighters were trying to put out a 2-alarm brush fire south of Thousands Oaks on Saturday, fire officials said.
The fire was reported around 1:38 a.m. near Trentwood Drive and Potrero Road, north of the Sherwood area, according to the Ventura County Fire Department.
Firefighters said the blaze had burned about 50 acres and was 30 percent contained as of 9:50 a.m.
The blaze, called the Potrero Fire, was the second blaze to occur in the Lake Sherwood area within the last 24 hours, said Capt. Mike Lindberry.
Fire officials said they were concerned about Santa Ana winds picking up this afternoon and planned to paint fire retardent to prevent the blaze from spreading.
Helicopters were making water drops as crews worked to knock the blaze on the ground.
About 330 firefighters were at the scene from five fire agencies. Agencies assisting with the firefighting efforts included Los Angeles County Fire Department, Cal Fire, San Bernardino County, and federal firefighters.
No injuries or evacuations were reported.