BEAVERTON, Ore. - A transformer caught fire at a PGE substation in Beaverton, causing more than 50,000 customers to lose power Saturday night.

Due to safety concerns, firefighters waited for the blaze to burn itself out, which they estimated could take between 12 and 18 hours.

As of 10:45 p.m., officials had restored power to about 20 percent of the customers who lost power due to the blaze. That included customers in Hillsboro, Banks, North Plains, West Union and Gales Creek, PGE said.

No one was evacuated and no nearby homes or apartments were threatened by the fire, which ignited at a substation at Southwest 158th Avenue and Southwest Jenkins Road about 7:45 p.m., PGE officials said.

The blaze caused PGE to "de-energize" the substation, which serves more than 50,000 customers in Hillsboro, Aloha, Beaverton, Banks and Gaston.

Fire officials said several explosions accompanied the fire, including one that launched a fireball 500 feet into the air.

About 25 firefighters initially responded but were pulled back from the blaze due to safety concerns, said Karen Eubanks, a spokeswoman for Tualatin Valley Fire and Rescue.

Officials were concerned about an explosive 10,000 to 20,000 gallon tank of mineral oil at the scene. The oil, which PGE said is non-toxic, is used for insulation and cooling.

They also feared firefighters getting electrocuted and were not spraying water or foam on the blaze, Eubanks said.

Firefighters Saturday night stood watch about 100 feet from the fire, which officials said was under control and contained in a fenced area.

Shortly before 11 p.m., PGE crews entered the substation and began repairing the damaged transformer.

Investigators aren't sure what started the blaze.

PGE said it was trying to get power restored to customers.

"As soon as we can isolate this incident, we can often serve those customers from a different source," said Gail Baker, a PGE spokeswoman.

The fire interrupted westside MAX service between Hatfield Government Center and Sunset Transit Center. However, officials planned to shuttle MAX riders by bus until power was restored.

The blaze ignited as PGE crews were still trying to restore power to those who lost electricity during Thursday's wind storm. As of 10 p.m., PGE reported 48,000 of those customers still without power.