At least 8,000 people have been displaced by an unpredictable Butte County, Calif., blaze that has destroyed 40 homes and 10 outbuildings, Sacramento station KCRA reported.

Authorities ordered residents of 3,200 Paradise homes to evacuate after the wind-stoked fire destroyed 40 homes and 10 structures Tuesday in the nearby rural community of Concow. Evacuation orders remained in effect for 1,000 residents of Concow and Yankee Hill, about 85 miles north of Sacramento.

Officials said more than 3,800 homes were threatened by the flames Wednesday. Another wildfire destroyed 74 homes in Paradise last month.

Two shelters were full Wednesday morning with 500 evacuees, said Melissa Smith, spokeswoman for the California Department of Forestry and Fire Protection, or Cal Fire.

The blaze had flared up early Tuesday after erratic winds blew embers across fire containment lines.

"Right now we're battling the weather and the erratic winds," said Todd Simmons, another Cal Fire spokesman. "Whatever the winds are doing, that's pretty much what the fire's going to do."

Firefighters were facing a sudden drop in humidity and a 10-degree spike in temperatures as a heat wave, forecast to linger until the weekend, grips much of the state.

About 30 lightning-sparked wildfires in Butte County, where Paradise and Concow are located, have charred 47,000 acres in recent weeks and were about 40 percent contained, officials said.

About 2,500 firefighters are battling the flames. Ten firefighters have suffered minor injuries.

Some people locked themselves in their homes Tuesday and refused to evacuate. They were counting on fire crews to protect them as the fire approaches.

Red Cross worker Vern Chadwick said it's been tough for those forced from their homes.

"Everybody's got to give a little bit," Chadwick said. "It's a tough situation when you shove that many people into one place."

In addition to heightening the fire danger, the recent heat wave in California raises concerns about heat illness among firefighters worn down by the long fight against blazes that have consumed more than 985 square miles in the state since late June.

"We do have a lot of fatigue because of the low numbers of resources in the state," said Thom Walsh, a Forest Service resource unit leader.

Crews took rest breaks in refrigerated trailers with bunk beds, Walsh said.

Highs are likely to be in the triple digits across much of the northern half of the state until at least Friday, National Weather Service forecaster Christine Riley said.

Temperature records for the date were broken in five cities Tuesday, including Sacramento, where the temperature reached 108, breaking the previous high of 104 degrees set in 1997. Modesto hit 107.