OAKLAND, Calif. -- PG&E crews in Oakland had a busy Friday morning after failed equipment led to an explosion and fire that knocked out power to some 4,000 east bay customers.

The incident happened in front of a large PG&E substation in the area of 21st Street and Telegraph Avenue at about 9:30 a.m.

Officials said a failed switch and cable triggered a small fire that charred a nearby tree.

Witnesses told KTVU they felt their building shake when the explosion happened.

“I saw a big explosion,” said Oakland resident Crystal Pervoe. “[It was an] atomic bomb looking thing and it was really loud. All of a sudden the bushes are on fire right by PG&E and all of a sudden a bunch of fire trucks and it was like really crazy.”

The incident also disrupted power to street lights, affecting traffic in the area. PG&E said power was restored to almost all of its affected customers.