SAN FRANCISCO — Fire crews joined aircraft from neighboring states today to battle hundreds of lightning-caused wildfires across Northern California.

One of the fires started by weekend thunderstorms had already blackened more than 10,000 acres — nearly 16 square miles — in a rural area of Lake County, about 120 miles north of San Francisco. No homes had been destroyed, but officials said voluntary evacuations were in place for residents of 36 homes.

Governor Schwarzenegger said he was told late Sunday evening that the state had 520 fires, and he found it “quite shocking” that by yesterday morning the number had risen above 700.

Moments later, a top state fire official standing at Schwarzenegger’s side offered a grim update. The figure was actually 842 fires, the assistant regional chief of the California Department of Forestry and Fire Protection, Del Walters, said. All but a couple were in the northern part of the state.

“This is an unprecedented lightning storm in California, that it lasted as long as it did, 5,000 to 6,000 lightning strikes,” Mr. Walters said. “We are finding fires all the time.”

A blaze that started at Napa County moved into Solano County as it burned over more than 6 square miles. It was 60%contained a spokesman for the California Department of Forestry and Fire Protection, Kevin Colburn, said.

No homes have been destroyed, and voluntary evacuations about 40 miles southwest of Sacramento have been lifted.

A blaze that had charred nearly 6 square miles at the Shasta-Trinity National Forest about 160 miles north of Sacramento was a threat to about 1,200 homes and several youth camps.

Assistance, mostly firefighting aircraft, had arrived from Nevada and Oregon in response to weekend requests. Mr. Schwarzenegger said he had enlisted the help “because you can never prepare for 500 or 700 or 800 fires all at the same time.”

Part of the reason for the swelling number of wildfires was that local and state officials were still counting after fierce thunderstorms Friday night touched off the blazes.

“We didn’t get real lucky with this lightning storm,” Mr. Walters said. “It wasn’t predicted — which often happens with these storms that come in off the Pacific, there’s no history of the weather as it approaches the shore — and so we got hammered.”

Mendocino County alone had 110 fires, with just 17 contained.

At Monterey County, a fire near the coast south of Big Sur was only 3% contained. It has consumed about 11 square miles acres since it was first reported yesterday.

Also in Monterey County, a wildfire west of King City at the Ventana Wilderness of the Los Padres National Forest was 66% contained. It has burned about 90 square miles.

The Ventana Wilderness fire, which started before the weekend lightning storms, led to an emergency airlift Sunday of eight endangered California condors. Coast Guard helicopters carried the seven juveniles and one adult bird from a wildlife center to the Monterey Airport.

At New Mexico, crews dropped 11,500 incendiary balls to ignite unburned vegetation and halt a blaze that has charred more than 49,000 acres, largely on grazing allotments on federal land.

Lightning started that fire today at the Lincoln National Forest about 20 miles southwest of Hope. It was not threatening any structures.

“The ranchers have already moved a lot of the cattle that were out there,” a U.S. Forest Service fire information officer, Deanna Younger, said. The grazing areas “will be the main loss,” she said.