A rapidly spreading wildfire chewed through a rugged Southern California mountain range on Thursday, destroying at least 10 homes, threatening more than 500 other residences and forcing some 1,500 people to flee.

Five people were injured as more than 1,000 fire-fighters, 13 helicopters and six air tankers battled the flames as they pushed eastward along the San Jacinto Mountains, a desert range 90 miles (145 kilometers) east of Los Angeles, Cal Fire Riverside Chief John R. Hawkins said.

A man near the origin of the fire suffered serious burns, Hawkins said. Four fire-fighters were also injured, including two who suffered heat exhaustion. Officials did not have details to release on the other two.

At least 10 homes have been destroyed and Hawkins said that number would likely triple as authorities make their way into the charred areas to assess the damage.

The fire was estimated at 17 square miles Thursday, with 10 percent containment, but it was growing, causing concern that the direction could change in the area, which is known as a wind tunnel.

“The conditions at the front right now are very dangerous,” Hawkins said.

Authorities still have not determined what caused the fire.

Evacuation orders were issued in five towns. Flames were marching toward the hardscrabble town of Cabazon, where hundreds scrambled to leave in the pre-dawn hours on Thursday as the mountain ridge behind their homes glowed red.

Many returned after sunrise to pack up more belongings and watch the flickering line of fire snaking along the brown, scrubby mountains.

Most of Southern California’s severe wildfires are associated with Santa Ana winds caused by high pressure over the West that sends a clockwise flow of air rushing down into the region.

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