California Governor Arnold Schwarzenegger has ordered over 6,600 residents in northern Los Angeles to evacuate, as more than 2,500 firefighters battle wildfires that have so far destroyed 18 homes, and threatened 12,000 other houses and critical infrastructure.

Despite low wind conditions, which would normally help in containing wildfires, the blaze doubled in size. Authorities attribute the rapid spread to dry undergrowth, which has accumulated during the past 40 years.

“It is still possible the fire will double again over the next several days,” U.S. Forest Service Capt. Mike Dietrich said (CBC News).

By the fifth day, the raging firestorm had destroyed over 130 square miles of vegetation; only five percent of the blaze had been contained.

Two firefighters died when their vehicle careened off a hill near the city of Acton. Advancing flames endangered communication towers and an astronomical observatory located on nearby Mount Wilson.

Elsewhere, several other wildfires burned in central and southern California. A blaze northeast of Sacramento destroyed numerous buildings, including homes in Auburn County. Residents in Oak Glen, approximately 90 miles from downtown Los Angeles, evacuated after fire approached the community. Fire also threatened to destroy 2,000 homes in San Bernardino County.

“In Mariposa County, a nearly seven-square-mile fire burned in Yosemite National Park and forced the evacuation of about 50 homes,” a park spokesperson said (The Associated Press).