The Portola Fire was reported around 2 p.m. in the 9800 block of West Portola Drive and it was said to be threatening homes in at least three neighborhoods.
Firefighters were mobilizing multiple engine companies to put structure defense in place.
More than 150 firefighters were assigned to the blaze, which had burned through more than 10 acres.
No injuries were immediately reported.
DEVELOPING: This story will be updated.