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Firefighters extinguish a smoldering tree at the site of a recent fire in northern California. Reuters/Robert Galbraith

A rapidly growing wildfire in California now covers 4,000 acres and is sparking mandatory evacuations.

Officials put in place mandatory evacuations for Red Dog, Chalk Bluff and You Bet, California, as well as the community of Cascade Shores, reports California Public Radio. Hundreds of homes are threatened, according to the California Department of Forestry and Fire Protection. The impacted areas so far -- parts of Nevada and Placer counties -- are roughly 70 miles northeast of Sacramento. Officials are setting up an evacuation center at a local high school.

Observers posted images of the conflagration on Twitter.

The National Weather Service says it expects the wind direction to shift Saturday night, bringing smoke from the fire eastward toward Nevada City, Grass Valley and the eastern Sacramento Valley into Sunday.

The cause of the wildfire is unknown. Investigators are asking the public for information about a vehicle of interest that was in the area at the start of the fire.

Firefighters are continuing to work on containing a separate fire that touched off on Wednesday east of Sacramento, California. That 6,900 acre fire is 55 percent contained, according to state officials.