A vegetation fire in northern California forced evacuations and destroyed 12 structures, according to officials. 

On Friday, the Shasta County Fire Department and CAL FIRE Shasta Trinity Unit reported that the Peter Fire had spread over 304 acres and is 35% contained.

As the blaze grew on Thursday afternoon, threatening a tortoise sanctuary, authorities said that challenging terrain and weather hampered firefighting efforts. 

CAL FIRE, or the California Department of Forestry and Fire Protection, said the blaze broke out mid-afternoon, just south of Redding. 

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It was not immediately clear how many of the burned structures were residences, but the Redding Record Searchlight newspaper reported that at least three homes were set ablaze.

Firefighters worked on the ground and in the air. 

The flames briefly threatened the Tortoise Acres sanctuary, which shared video of the fire and images of people loading tortoises into vehicles.

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An evacuation center was set up at a local high school. 

The cause of the Peter Fire remains under investigation.

According to the National Interagency Fire Center, more than 6,200 wildland firefighters and support personnel are assigned to incidents nationwide. 

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Since Jan. 1, 36,578 wildfires have burned 5,179,043 acres – well above the 10-year averages of 29,931 wildfires that burned more than 2,7 million acres. 

The Associated Press contributed to this report.