A forest fire has scorched nearly 3,000 hectares (7,400 acres) in a mountainous area near San Diego, California, as fire fighters said Monday they had only gotten the blaze five percent under control.

The US Forest Service said the fire began Sunday morning, and that the source was a campfire, likely set by persons crossing the nearby US-Mexico border illegally.

Five hundred firefighters battled the blaze under scorching temperatures reaching 40 degrees C (104 degrees F) and with high winds, and two were slightly injured.

About 150 homes were evacuated, but no damage to buildings was reported immediately.

"The overall plan is to use air tankers in the northern parts of the fire and helicopters in the southern parts of the fire," according to Cleveland National Forest spokeswoman Roxanne Provaznik.