SAN FRANCISCO, United States (AFP) — A Californian wildfire that began on the weekend has rapidly spread across 70,000 acres (28,000 hectares), authorities said Tuesday, with a growing number of areas affected by mandatory evacuation orders.

The county fire was sparked in the northern Yolo County on Saturday, fanned by high winds and hot temperatures. 

An update by Cal Fire on Tuesday said the potential for growth remains high as crews battle the fire in difficult terrain. 

“Firefighters continued to work through the day to construct new containment lines and defend structures impacted by the fire,” the authority said, noting that only five per cent of the fire had been contained.

More than 2,000 firefighters are now involved in battling the blaze, deploying 187 fire trucks and 18 helicopters.

Another blaze — the Pawnee Fire affecting Lake County, had burned 14,500 acres and destroyed 22 buildings, but was 80 per cent contained as of Sunday.

Last year was California’s deadliest on record for fires.

The Thomas fire, in the Santa Barbara area in December, killed two people, destroyed more than 1,000 buildings — including multimillion-dollar homes — and torched some 259,000 acres. It was deemed the third most destructive blaze since 1932.

October fires in the wine regions of Napa and Sonoma valleys, north of San Francisco, killed some 40 people, razed some 245,000 acres of forest and scrub, and destroyed more than 7,000 homes and buildings.

Experts say that global warming increases the risk of out-of-control blazes by drying out vegetation, making it more inflammable and easily set alight by lightning, spontaneous combustion, or fires lit by humans.