California's largest wildfire this year has claimed two lives after exploding in size over the weekend and forcing thousands to evacuate their homes.

Firefighters in the state's north battled to gain control of the McKinney Fire on Monday.

Whipped up by strong winds and lightning storms, the fire ripped through the state's dry terrain on Sunday to spread over some 52,500 acres of Klamath National Forest near the town of Yreka — and was zero percent contained as of Sunday night according to the California Department of Forestry and Fire Protection.

It had broken out Friday near the border with Oregon. 

Emergency declared

Nearly 650 people were working to douse the blaze as of Sunday, the National Wildfire Coordinating Group said.

California Governor Gavin Newsom has declared a state of emergency, saying the fire threatens "critical infrastructure."

More than 2,000 residents of rural neighbourhoods in the area were under evacuation orders, according to the California Office of Emergency Services, mostly in Siskiyou County.

The US Forest Service said thick smoke had helped to limit the growth of the fire on Sunday, but also meant that firefighters' aircraft were "mostly grounded."

California, which is facing a punishing drought, still has months of fire season ahead of it. The state and other parts of the western United States have been ravaged by huge and fast-moving wildfires in recent years, driven by years of drought and exacerbated by a warming climate.

Source: agencies