At least six people have died and thousands evacuated as an unusual lightning storm has sparked nearly 400 fires across Northern California in the last few days. U.S. President Donald Trump has declared that wildfires burning through homes and devastating precious forestry in California are a major disaster and he has released federal aid, local media reported on Sunday.

More than 13,000 firefighters are battling 585 fires that have burnt nearly 400,000 hectares. Nearly 41,000 residents in Sonoma County were under evacuation warnings or orders Saturday, officials said, adding that an evacuation order on Saturday extended to thousands of people in the Bay area near San Jose and warned others to be prepared to abandon their homes at short notice.

Forecast high winds are threatening to drive flames into more populated areas as foul air blankets the state. Firefighters dug a fireline around the University of California Santa Cruz campus as flames came within a mile of the buildings and surrounding area.

The National Weather Service has issued air quality alerts for parts of at least six states: California, Nevada, Oregon, Idaho, Colorado and New Mexico. These alerts warn of moderate to heavy smoke, and advise people – especially those with heart disease or respiratory illnesses – to consider staying indoors and limiting outdoor activity.