CLAYTON -- Authorities on Sunday ordered dozens of residents near the growing wildfire burning outside Mt. Diablo State Park to leave their homes immediately and take only essential items and pets.

At least 800 acres of vegetation had burned on Morgan Territory Road, and the Contra Costa County sheriff's officers ordered all residents and people on Oak Hill Lane, Curry Canyon Road and the Curry Point area to leave immediately as the fire continued to burn with 10 percent containment by about 7:30 Sunday evening.

"Leave now by car. Go by way of Morgan Territory Road. Take only those essential items you have ready and can carry with you. Pets must be in a carrier or on a leash. Lock your windows and doors as you leave. Stay off the phone unless you need to report a life-threatening emergency at your location," said Sheriff's Office spokesman Jimmy Lee.

As many as 75 homes were in danger and possibly more as the fire shifts to the south away from the Clayton area. The fire area is thick with brush on rugged mountain terrain. The blaze's cause is unknown.

Just after 11:45 p.m. Sunday, Lee said residents of the following areas were evacuated as well: Trail Ride Road, Russelmann Park Road, East Trail Road, Upper Trail Road and Lower Trail Road.

He said there were about 24 homes in those areas and most of the residents had already been evacuated by emergency personnel.

People who evacuated were told to go to the Clayton Community Library, 6125 Clayton Road in Clayton, and those with disabilities who cannot leave their homes on their own were to call 911 immediately, Lee said.

More residents could face evacuations.

Bill Chase, who lives on Whispering Pines Road, was collecting his valuables and spraying down his roof and fence with water even before the evacuations were ordered.

"Its been pretty wild out here," he said.

Fueled by temperatures in the 90s and only a slight breeze, the fire Sunday evening was moving in a southerly direction along the Mt. Diablo State Park boundary, said CalFire Battalion Chief Mike Martin.

Clayton Mayor Julie Pierce said, "Everyone is flashing back to the fire of '77. We're hoping it's not as bad as that."

On Aug. 2, 1977, after two years of drought and two lightning strikes that day, a fire charred 6,000 acres on the entire north side of Mount Diablo.

On Sunday night, more than 250 firefighters were battling the fire.

The fire began shortly after 1:45 p.m. and was reported at Morgan Territory and Marsh Creek roads, sending massive plumes of white and dark smoke over most of Contra Costa County.

People on social media sites reported seeing smoke in Vacaville, Richmond, Tracy and even at Candlestick Park, where the San Francisco 49ers were playing their opening game.

"This thing grew pretty quickly," said Dave Miller, who left the Oakland A's game early Sunday to check on his Morgan Territory Road home. "Now the wind is picking up; it could get ugly."

At 6:30 p.m., the fire was moving uphill away from his home, but everyone was on edge. Miller's next-door neighbor, Lisa Keenan, said the fire grew quickly after she first saw the smoke. "It just broke into flames,'' she said.

Karen Cooper, who works at a dog kennel on Morgan Territory Road, safely evacuated 20 dogs. But two of her horses, Butter and Pineapple, were missing Sunday evening, she said. "It's been intense."

Firefighters from CalFire, the San Ramon Valley Fire District, the Contra Costa Fire District and the East Bay Regional Park District are battling the blaze, the largest fire near Mount Diablo in recent history.

Contact David Debolt at ddebolt@bayareanewsgroup.com. Follow him at Twitter.com/ddebolt. Reach Kristin J. Bender at kbender@bayareanewsgroup.com. Follow her at Twitter.com/kjbender. Reach Rick Hurd at rhurd@bayareanewsgroup.com. Follow him at Twitter.com/3rderh.