Thousands of people evacuated during a Northern California wildfire were allowed to return home Thursday afternoon as crews continued battling flames amid scorching heat, officials said.

Containment of the Thompson Fire near the city of Oroville in Butte County also increased to 29% from 7%.

The “vast majority” of the 17,000 people under evacuation orders or warnings were able to go home, said Kristi Olio, public information officer for Butte County. Previous reports of 26,000 people being under orders or warnings were inaccurate, she said, adding that the fire has unfolded so quickly that it has been difficult to get firm figures.

Related story: Yes, wildfires are actually becoming more intense and more common, study says

The Thompson Fire broke out before noon Tuesday about 70 miles north of Sacramento, sending up a huge plume of smoke that could be seen from space. The fire had burned 5.9 square miles, up from 5.5 square miles earlier Thursday.

But officials warned of hot temperatures that could hit 108 degrees Fahrenheit with even hotter weather expected Friday and Saturday.

“The winds are slowly picking up,” said Chris Peterson, information officer for the California Department of Forestry and Fire Protection, or Cal Fire. “You add that with the heat and low humidity,” and the potential for volatile fire behavior grows.

Four structures were destroyed, and more than 12,000 were threatened. Cal Fire did not specify if the structures were homes, but an Associated Press photographer saw fire burn three adjacent suburban-style homes in Oroville.

Four firefighters reported injuries, all from heat. The cause of the blaze was being investigated.

Related story: Wildfire in Los Angeles County scorches through 16,000 acres

The region is familiar with catastrophic events. The deadliest and most destructive wildfire in state history nearly wiped out the town of Paradise in Butte County in 2018. And in 2017, both spillways of the Oroville Dam — the nation's tallest — failed, mandating the evacuation of nearly 200,000 people.

"We do it ‘well,’ I guess, is the word to say,” said Oroville Mayor David Pittman.

He said the 20,000 residents of Oroville have heeded evacuation warnings and stepped up to offer a place to stay and home-cooked meals for evacuees.

Millions of people across the U.S. are baking in a heat wave including in California, which is seeing “significantly more wildfire activity at this point” than in recent years, California Gov. Gavin Newsom's office said in a statement.

More than a dozen other blazes, most of them small, are active across the state, according to Cal Fire. The largest of those, the Basin Fire in Fresno County, was nearly 50% contained with 22 square miles burned.