A fire late Saturday at a Los Angeles Department of Water and Power facility forced officials to cut off power to about 140,000 city residents, leaving them without air-conditioning for hours during a record-breaking heat wave.

The fire, which broke out at a receiving station in the northern Los Angeles neighborhood of Northridge around 9:53 p.m., burned intensely on and around high-voltage equipment, said Brian Humphrey, a spokesman for the Los Angeles Fire Department. Columns of smoke billowed over the San Fernando Valley as firefighters worked for about two hours to extinguish the blaze, he said.

The fire left grid operators with no choice but to shut down power so that crews could safely put out the flames.

Officials said in a statement that the energy transmission system in the northern part of the city “was significantly disrupted by the fire and subsequent outage.”

“Once the fire is out and the system is stabilized, crews will work to re-energize affected areas as quickly as possible,” the Los Angeles Department of Water and Power, which is the nation’s largest municipal utility, said in the statement. Until the extent of the damage can be assessed, “it is not possible to estimate the time for service restoration,” the statement said.

By about 1 a.m. Sunday, crews had restored power to almost 50,000 customers, the utility said on Twitter.

The power outage could scarcely have come at a worse time for Angelenos, who have been suffering for days in a heat wave that reached new highs on Saturday.

Curt Kaplan, a meteorologist with the National Weather Service in Oxnard, Calif., said downtown Los Angeles recorded a temperature of 98 degrees on Saturday, breaking a record of 95 degrees for the day that was set in 1886. Elsewhere, decades-old records were nearly broken; Woodland Hills, a Los Angeles neighborhood near where the fire broke out, reached 112 degrees, tying a record from 1985.

Some miserable residents took to Twitter to vent their frustration, using the hashtag #LAHeat.

“Every person we contact is complaining,” Mr. Humphrey said.

The high temperatures have contributed to about a dozen fires that are raging across California, officials and experts said. The largest is the 19,000-acre Alamo fire in San Luis Obispo County, which is only 10 percent contained, said Lynnette Round, a spokeswoman for the California Department of Forestry and Fire Protection.

Another fire, in Butte County in Northern California, has forced some mandatory evacuations, according to the department.

California was drenched with rain this winter after suffering through years of drought. Weather and fire experts said the precipitation left behind brush and foliage that now makes it easier for fires to spread quickly.