Los Angeles: As some residents whose homes were threatened by a vast Southern California wildfire were allowed to return home, forecasters warned that the cooler, damper conditions that have aided recent firefighting efforts would soon turn in favour of the flames.

Mike Smith, a meteorologist with the National Weather Service in Sacramento, said that over the next couple of days, California's coastal regions would get warmer temperatures and offshore breezes that would keep moist marine air from coming inland.

More than 2,000 residents were allowed to return Monday to their homes in Goleta, said Roger Aceves, the city's mayor pro tem.

But some mandatory evacuation orders and warnings to be ready to leave remained in effect for scattered homes on the fire's growing western flank on the Santa Ynez Mountains, Aceves said.

Five fresh crews, totalling 100 firefighters, were brought in Monday to help. Firefighters had contained 35 per cent of the fire in the Los Padres National Forest that is threatening the city, mainly on its southern side bordering neighbourhoods.