LOS ANGELES >> Electricity is slowly being restored Sunday to tens of thousands of customers who lost service when a power station in suburban Los Angeles caught fire amid a blistering heat wave.

The LA Department of Water and Power said it hopes to restore electricity to all customers by late Sunday morning.

Crews worked through the night to repair conductors, circuit breakers and transformers damaged in the blaze. The fire’s cause is under investigation.

At its height, the outage Saturday evening affected 140,000 customers in the northeast San Fernando Valley. Cooling centers were opened for residents left without air conditioning.

The fire at the station in the Northridge/Reseda area involved equipment that carries high-voltage electricity and distributes it at lower voltages, the department said.

The department shut off power to the station as a precautionary move, and began restoring service once the flames were out.

The outage came as much of California baked in heat that broke records. A record that stood 131 years in Los Angeles was snapped when the temperature spiked at 98 degrees downtown.

Shortly after the blaze broke out, crews found a huge container of mineral oil that is used to cool electrical equipment on fire, Fire Department spokesman Brian Humphrey said.

“These were fierce flames, with smoke towering more than 300 feet into the sky,” he told the Los Angeles Times.

No one was injured.

Firefighters rescued people who were stranded in elevators, Humphrey said.

People reported losing power in neighborhoods including Porter Ranch, Winnetka, West Hills, Canoga Park, Woodland Hills, Granada Hills, North Hills, Reseda and Chatsworth.