Bay Area wildfire has scorched more than 3,700 acres

Two new wildfires begin in California 0:25

A wildfire that sparked Sunday in the hills east of San Francisco Bay had charred more than 3,700 acres by late Monday, authorities said, as it became just the latest front in California’s summer-long fire fight.

Some 700 state and local firefighters battling the so-called Morgan Fire had brought containment up to 20 percent Monday afternoon, a jump from 10 percent in the morning. And while only one far-flung outbuilding had burned, NBC Bay Area reported, the fire still loomed some 100 area homes.

“The fire has grown significantly,” Cal Fire Division Chief Dave Shew told NBC Bay Area. It more than doubled in size from early Monday’s scorch zone of 1,500 acres.

Shew could not estimate when the fire might be fully contained, according to NBC Bay Area. But he told the station that the region may clear up by Wednesday.

While the fire rapidly expanded, fire crews worked furiously to beat back the flames from a Pacific Gas and Electric (PG&E) transmission line, communications infrastructure on the tip of the mountain and historical buildings near the center of the blaze, according to the station.

On Monday morning, the fire had nearly reached the summit of 3,800-foot Mount Diablo, prompting the need for more fire personnel.

The latest incident reports said that there are now 85 fire engines, 30 fire crews and two air tankers working to mitigate the blaze.

Aerial footage from NBC Bay Area’s helicopter showed intense, raging flames and thick, billowing smoke shooting from around the mountain top. 

Cal Fire ordered mandatory evacuations Sunday for areas in and around Clayton, a community of 11,000 people. Fifty to 75 homes were threatened by the swiftly moving flames, it said.

A helicopter sprays water as vegetation burns on the east side of Mount Diablo, near Clayton, Calif., on Sunday. The fire grew to 1,500 acres by Monday morning. Peter Dasilva / EPA

“Leave now by car," the Contra Costa County Sheriff's Office said in an advisory marked as "urgent" about 6 p.m. "... Stay off the phone unless you need to report a life-threatening emergency at your location.”

One injury has been reported. The name of the person has not been released and the cause is currently under investigation.

The Clayton Community Library has been set up as an evacuation center, and the Contra Costa County Fairgrounds is being used as a safe place to take horses, cattle, hogs, sheep and goats.

NBC Bay Area contributed to this report.