Rain and cooler temperatures in California's rugged Sierra Nevada brought welcome relief on Thursday to fire crews battling flames that have destroyed a dozen homes and threatened thousands more during the past two weeks near Lake Tahoe.

A firefighting force now numbering 8,000 personnel, the most ever deployed against a single California wildfire, had carved buffer lines around 43 percent of the blaze's perimeter as of Thursday morning, fire command spokesman Mike McMillan said.

That figure was up sharply from the 10 percent containment level reported at the start of the week, and additional evacuation orders were lifted late on Wednesday, though 2,000-plus people remained displaced by the blaze, McMillan said.

The King Fire has charred nearly 150 square miles of drought-parched timber and brush in two national forests since it erupted on Sept. 13 along the south fork of the American River, southwest of the Lake Tahoe resort area.

A 37-year-old man accused of starting the fire was arrested last week on arson charges. He has pleaded not guilty.

The blaze was stoked early on by extremely low humidity, strong, erratic wind gusts and a heat wave that baked much of California for more than a week.

A break in the weather days ago brought cooler, moister conditions and lighter winds that helped firefighters gain ground against the flames.

A midweek Pacific storm chilled temperatures further and ushered showers into the region on Thursday, with as much as a half-inch of rain expected to fall over the fire zone, McMillan said.

"We're making excellent progress and continuing to see the containment rise every day," he said. "We're going to capitalize on this wet weather and continue that."

The King Fire has proven costly, with authorities spending an estimated $1.6 million to date on the blaze.

Twelve homes and nearly 60 outbuildings have been destroyed, and 12,000 dwellings were still listed as threatened. There have been no fatalities but six people have been reported hurt, all firefighters with non-life-threatening injuries.

At its peak last week, the King Fire ranked as the most menacing of nearly a dozen major wildfires across California. While the statewide fire threat has since subsided, the King still topped a list of nine large blazes under full-scale attack throughout the West, according to the National Interagency Fire Center in Idaho.