LOS ANGELES • Firefighters struggled to contain infernos across the western United States as experts warned that drought-stricken California should prepare for an unusually intense wildfire season.

Forest fires are a fact of life in much of California but have become far worse because of bone-dry conditions, with the Golden State gripped in its fifth year of drought.

A fire in the Los Padres National Forest had expanded to 5 sq km by Thursday, making it the "largest since 2009" in the area, a spokesman for the Santa Barbara County Information Centre told AFP.

Strong winds were hampering efforts to contain the blaze, and the operation was expected to be hindered further by near-record temperatures over the weekend in the southern half of California.

Los Padres, which begins about two hours' drive north-west of downtown Los Angeles, is popular with hikers and campers, and evacuation orders were issued in at-risk parts of the forest.

Sections of Highway 101, which links northern and southern California, were temporarily closed while oil giant ExxonMobil evacuated its refinery in Las Flores Canyon.

Another fire further north burned about 10 sq km and caused road closures.

Last month, fires near Los Angeles pushed 5,000 people out of their homes in the affluent Calabasas area.

AGENCE FRANCE-PRESSE