Five people were hurt and revelers scrambled for safety when a series of explosions in an underground electrical vault sent flames shooting into the sky during an Oktoberfest celebration at a shopping and dining complex in Southern California, authorities said Sunday.

Two firefighters and two restaurant employees were treated for minor injuries following the blasts around 8:15 p.m. Saturday during the annual event at Old World Village in Huntington Beach, according to Battalion Chief Jeff Lopez with the city’s fire department. A third restaurant employee had moderate to severe injuries, he said.

Firefighters were initially called to the scene for a reported electrical fire in the underground vault. The first explosion splattered heated mineral oil used to cool the transformers and possibly ignited subsequent blasts, authorities said at a Sunday press conference. The cause is under investigation.

Witnesses said they heard as many as three explosions coming from the festival about 35 miles (62 kilometers) south of downtown Los Angeles.

Megan Houck, 26, said she saw flames come up from the floor near a patio area.

“It was just like one giant fireball that went up,” she told the Long Beach Press Telegram. “And then there was a second explosion maybe 10 or 20 seconds later.”

Houck said the flames went well above the roof of the village, up to 40 feet (12 meters) in the air.

Revelers, some wearing traditional German costumes including lederhosen, ran from the scene as police evacuated the complex.

Southern California Edison crews worked through the night to replace three damaged transformers in the vault and restore power, spokesman Robert Villegas said. As many as 1,700 customers lost electricity, he said.

Pat Brassil, 27, said he was outside one of the Oktoberfest tents when he saw flames shoot out from another tent near the festival’s entrance.

“It just lit up the sky,” he told the Los Angeles Times. “Everyone was going pretty crazy and screaming.”