Fire crews responded to a two-alarm brush fire near San Bruno Mountain on Thursday.
The fire was reported about 3:30 p.m. at Guadalupe Canyon Parkway and Bayshore Boulevard in Brisbane, fire officials said. It was burning brush and trees near two roadways at the foot of San Bruno Mountain.
When firefighters arrived, the blaze covered about 1 to 2 acres between southbound Highway 101 and Bayshore Boulevard. A second fire started across the freeway on the northbound side of 101, according to the South San Francisco Fire Department.
No structures were threatened and no injuries were reported, fire officials said. But traffic on 101 was quickly backing up as the afternoon commute was beginning.
San Mateo County's Alert system warned motorists to avoid 101 at Cow Palace and Bayshore Boulevard due to the fire.
Crews from South San Francisco, Brisbane, Daly City and Cal Fire were at the scene.
The cause of the fire is under investigation.