JURUPA VALLEY, Calif. -

Despite 25-mile-per-hour winds, crews today expanded their containment lines around a brush fire that started on the Jurupa Valley side of the Santa Ana River bottom, scorching 311 acres and damaging two structures.

The non-injury fire, which broke out about 4:45 p.m. Thursday at Rio Road and Calle Hermosa, on the edge of Rancho Jurupa Park, was 40 percent contained by 1 p.m. today., according to the Riverside County Fire Department.

The National Weather Service issued a wind advisory until 10 a.m. Saturday, forecasting an offshore breeze of 15 to 25 mph, with gusts up to 45 mph below canyons and passes. Humidity was below 15 percent in the Riverside area this afternoon.

The South Coast Air Quality Management District issued a smoke advisory, warning that people in vulnerable health and children in Riverside, Jurupa Valley and other communities should stay indoors as much as possible.

Nearly 200 firefighters from Riverside and Orange counties, the Pechanga and Morongo Indian Reservations, and the cities of Riverside, Murrieta and Corona, as well as inmate hand crews, worked to surround the fire. There was no word on when it might be fully contained.

A water-dropping helicopter was making periodic runs on the fire today. Flare-ups were reported in multiple locations as brush continued to smolder.

Thursday evening, a mobile home about a quarter-mile downwind from the main fire burst into flames, but no one was injured. A storage building also was damaged, and nearby homes were threatened, but crews mustered all available resources to prevent the properties from burning.

The Riverside Fire Department called for voluntary evacuations of homes Thursday in the area of Grassy Trail Drive, Greenbrier Drive and Old Mill Road, all of which abut Anza Narrows Park. The evacuation request was lifted a few hours later. Access to some riverbank locations frequented by joggers and bicyclists was shut down.

There were initial reports that downed power lines may have triggered the fire, but officials could not confirm a cause.

Approximately 1,846 Riverside residents lost power during the blaze, said county fire spokeswoman Jody Hagemann. Service was restored overnight.