California firefighters, helped by aircraft, battled a wind-driven wildfire that continued not only burning but spreading on Sunday, in an area straddling the San Francisco Bay Area and central California, authorities said.

The Corral Fire began on Saturday near the city of Tracy, 60 miles east of San Francisco, and the Lawrence Livermore National Laboratory in the city of Livermore, according to the California Department of Forestry and Fire Protection, or Cal Fire.

Dark plumes of smoke travelled high into the sky over the fire area, made up mostly of grassy hills.

On Sunday the blaze appeared to be growing, fuelled by hot and dry conditions.

Cal Fire updated the size of the fire to 19.5 square miles, up from 17.2 square miles on Saturday.

The fire was 15% contained as of Sunday morning, the Cal Fire Santa Clara Unit said in a Facebook post, adding that strong winds and dry grass “have made it difficult for firefighters to contain”.

Chief Baraka Carter said two fire workers were injured, the San Francisco Chronicle reported.

The National Weather Service said “dangerously hot conditions” with highs of 39.4C to 42.2C were expected later in the week for San Joaquin Valley, an area that encompasses the city of Tracy.

Wind gusts of up to 45mph hit the region on Saturday, according to meteorologist Idamis Shoemaker of the NWS Sacramento.