SACRAMENTO, California - A rapidly moving fire in Northern California had burned about 1,620 hectares of land by Saturday morning and prompted evacuations of thousands of residents, some of whom were also injured.

The blaze, called the Mill Fire, started on Friday nearly 370km north of Sacramento.

By Saturday morning, it was about 20 per cent contained, according to the California Department of Forestry and Fire Protection.

About 100 homes and buildings were reported destroyed by the fire, authorities said.

California Governor Gavin Newsom proclaimed a state of emergency for Siskiyou County. The emergency declaration will help residents access federal aid and unlock state resources.

Newsom's office said the fire had caused civilian injuries and power outages, destroyed homes and forced thousands of residents to evacuate. Local officials said people should plan for "at a minimum several days" to stay away from evacuated areas.

Siskiyou County, home to Klamath National Forest, has a population of about 44,000, according to the US Census Bureau.

Kim Greene, the mayor of the small city of Weed in Siskiyou County, told the Los Angeles Times that the fire started at a lumber mill.

Videos posted on Twitter by local media and journalists showed the fire destroying an industrial building in Weed, burning forested land and spreading through residential areas.

Another fire called the Mountain Fire was also simultaneously spreading in Gazelle, located 16km north-west of Weed.

As of Saturday morning, that fire was only 5 per cent contained and had burned about 1,375 hectares of land.

More than two decades of drought and rising temperatures, exacerbated by climate change, have made California more vulnerable than ever to wildfires.

The two most devastating years on record were in 2020 and 2021, based on the number of acres burned. REUTERS