California officials declared a state of emergency Monday in the area near Lake Tahoe where firefighters battled a raging forest fire that has destroyed 225 buildings and forced the evacuation of hundreds more.

The disaster declaration makes portions of El Dorado County eligible for immediate state aid, and is the first step in requesting emergency federal assistance to fight the blaze, which rained ash on the pristine lake and darkened skies in the high Sierra.

"The circumstances of this wildfire, by reason of their magnitude, are beyond the control of the services, personnel, equipment and facilities of any single county," said Lt. Gov. John Garamendi, who signed the proclamation declaring the emergency Monday while Gov. Arnold Schwarzenegger was in Europe.

The blaze, believed to be caused by humans, was approaching 2,500 acres - nearly 4 square miles - and was less than 10 percent contained Monday, said Lt. Kevin House of the El Dorado County Sheriff's Department. No injuries were reported.

The number of firefighters battling the blaze nearly doubled, to about 800, on Monday morning, as officials also stepped up an aerial assault, using nearly a dozen tankers and helicopters to drop water and retardant over the heavily wooded, parched terrain.