An unwelcome change in the weather, with higher winds, temperatures and lightning that threatens to spark new wildfires was coming on Sunday to parched Northern California, where firefighters have for nearly a week battled three huge "complexes" of fires that have destroyed hundreds of homes and forced thousands to flee.

Responding to the emergency, President Donald Trump issued on Saturday a major disaster declaration to provide federal assistance. Governor Gavin Newsom said the declaration will also help people in counties affected by the fires with crisis counseling, housing and other social services.