SAN FRANCISCO — A series of fast-moving fires in the San Francisco Bay Area and elsewhere in Northern California — many caused by intense lightning storms — exploded overnight, burning homes and causing thousands to flee.

The newest fires stretched from the wine country to the Santa Cruz Mountains, moving with ferocious speed amid an intense heat wave that also has brought rolling blackouts. Smoke from the fires has caused terrible air quality across the region.

Many of the fires were believed to have been caused by lightning strikes. Northern and Central California began experiencing an unusually active sequence of largely dry lightning strikes Sunday morning, the most widespread and violent in recent memory in the Bay Area on one of the hottest nights in years, according to Daniel Swain, a climate scientist with the University of California, Los Angeles and the National Center for Atmospheric Research.

Over the last 72 hours, there have been more than 10,800 lightning strikes statewide, causing roughly 367 new fires, according to the California Department of Forestry and Fire Protection, or Cal Fire.

The rapid outbreak of new blazes has stretched the state’s firefighting resources to their limit.

Jeremy Rahn, the lead Cal Fire public information officer for the LNU Lightning Complex fire, said Wednesday that the state had already requested 375 additional fire engines as well as additional hand crews from out-of-state agencies, and hired “nearly all available private firefighting ‘call when needed’ aircraft in the western United States.”

“The size and complexity at which these incidents are burning is challenging all aspects of emergency response,” he said during a media briefing Wednesday.

Solano County was facing serious threat after fire caused residents to flee overnight and burned homes and other structures.

Officials have ordered the evacuation of the western edge of Vacaville — a city of 100,000 residents about halfway between San Francisco and Sacramento — in the area of Alamo Drive north of Interstate 80 and west of North Orchard Avenue, according to a Facebook post by Vacaville police. The Vacaville Fire District also ordered evacuations of Pleasants Valley Road, which lies west of the city, and the English Hills area north of the city.

A KPIX-TV reporter on Pleasants Valley Road, with flames visible on hills in the background, described windy conditions and embers blowing toward the south. The reporter tweeted a video of a home burning off Pleasants Valley Road.

The blaze threatening Vacaville was among a number of fires constituting the LNU Lightning Complex fire, which has burned more than 46,000 acres in Napa, Sonoma and Solano counties. The largest blazes within the LNU Lightning Complex include the Hennessey and Gamble fires, which began in the mountains east of the northern Napa Valley and west of Lake Berryessa.

As of Wednesday morning, 50 structures had been destroyed, 50 more had been damaged and 1,900 were threatened, fire officials said.

At 11 a.m. PDT, officials issued an evacuation order covering parts of Napa County, warning of an “immediate threat to life.” An evacuation warning has also been issued for portions of Sonoma County.

Another rapidly growing fire was burning in the mountains southwest of Silicon Valley, on the border of San Mateo and Santa Cruz counties.

Evacuations were ordered around Big Basin Redwoods State Park, Ano Nuevo State Park, Butano State Park and Pescadero Creek Park. The CZU August Lightning Complex — which consists of 22 fires — has burned at least 10,000 acres and forced the evacuation of more than 22,000 people, officials said Wednesday.

“Last night, we saw a major increase in fire activity throughout both San Mateo and Santa Cruz counties, and we saw several of the fires merge together,” Cal Fire Deputy Chief Jonathan Cox said during a briefing Wednesday morning.

Flames are generally burning toward the southeast, from the San Mateo County line into Santa Cruz County, he said.

“This is a very active timber fire burning in two counties,” he said, “with a serious threat to both public safety and for structures that are out in front of it.”

Additional evacuations were ordered early Wednesday in Santa Cruz County around Bonny Doon, including Pine Flat Road South. An evacuation center has been set up at the Santa Cruz County Fairgrounds in Watsonville.

On Tuesday, Gov. Gavin Newsom declared a statewide emergency in order to help California respond to the outbreak of fires. More than 30 major wildfires are burning across California, according to Cal Fire officials and a Los Angeles Times analysis.

Newsom’s office said the state had secured assistance from the Federal Emergency Management Agency to respond to fires in Napa, Nevada and Monterey counties.

“We are deploying every resource available to keep communities safe as California battles fires across the state during these extreme conditions,” Newsom said. “California and its federal and local partners are working in lockstep to meet the challenge and remain vigilant in the face of continued dangerous weather conditions.”

The rash of fires has also led to a spike in traffic to Cal Fire’s website, overloading it and intermittently crashing it, officials said. Cal Fire personnel were working with their technology department Wednesday morning to try to handle the crush of visitors.

Another blaze, dubbed the Dolan fire, has grown to an estimated 2,500 acres and prompted evacuations in Monterey County near Big Sur.

As of Wednesday morning, the fire was “actively burning in all directions,” according to Los Padres National Forest officials. Because of the fire, Highway 1 has been closed from Ragged Point in San Luis Obispo County to Julia Pfeiffer Burns State Park in Monterey County, officials said.

The River fire, also in Monterey County, has burned through more than 4,000 acres and has already destroyed six structures and damaged two others, according to the California Department of Forestry and Fire Protection. More than 1,500 structures remain threatened by the blaze, which has prompted mandatory evacuations.

A cluster of fires is also burning in sparsely populated, mountainous terrain east of Silicon Valley and the East Bay and west of the Central Valley. This grouping, the SCU Lightning Complex fire, began early Sunday. It has burned at least 85,000 acres in five counties — Alameda, Contra Costa, Santa Clara, Stanislaus and San Joaquin.

Temperature records for the day were broken across California on Tuesday, with Woodland Hills hitting 112, breaking a record last set for Aug. 18 in 1949.

Other spots that reached record temperatures for the day included Needles (118), Barstow (113), Paso Robles (111), Sacramento (109), Merced (107), Modesto (106), Anaheim (105), Gilroy (104), El Cajon (102), Long Beach (100), UCLA (97), Camarillo (95), Oxnard (90) and Newport Beach (87). Riverside hit 108, tying a record for the day last set in 1950.