Courtesy Kelly Fang / The Daily Californian Smoke pours out of a grate after an explosion at the University of California, Berkeley campus on Monday.

An explosion and a power outage prompted a campus-wide evacuation at the University of California, Berkeley on Monday.

Fire officials said an explosion in a generator vault was reported at 6:40 p.m.

Student Colin Ho was walking on campus when the electrical explosion erupted, sending flames shooting into the sky.

"Essentially there was a massive fireball that erupted," Ho said. "The fireball was two times the height of the building, and everyone just got the hell out of there."

Campus officials said the explosion sent one person to the hospital with minor injuries. Three other people suffered minor burns from the fire but were treated at the scene.

The explosion happened at an underground electrical vault outside California Hall near the center of campus as crews were attempting to repair damage caused by a copper wire theft last week, a campus spokesman said.

Power being restored to the equipment sparked the explosion. It was believed damage was repaired prior to the explosion, but officials said the damage was more extensive than first thought.

"The explosion occurred when university engineers were bringing power back online," said Dan Mogulof, UC Berkeley spokesman. "It now appears the damage caused by these unknown individuals was far more extensive and far more significant than seen and assessed."

Campus officials canceled classes Monday night and sent out an emergency message to students' cellphones and email inboxes alerting them of the explosion and telling them to leave the main campus area immediately. It is still unknown if classes will resume on Tuesday.

More than a dozen students couldn't leave the campus because they were stuck in elevators during the outage.

Alix Martichoux, an NBC Bay Area intern who attends UC Berkeley, said in addition to the email and text alerts, campus officials were telling everyone to evacuate the campus over a loudspeaker.

As of 7 p.m., firefighters were still working to put out flames inside the generator vault. The fire was extinguished later that evening.

By 8 p.m. campus officials reported that anyone who had been trapped in an elevator during the outage had been rescued.

"As of yet, we don't know if classes are on for tomorrow. For updates, call 800-705-9998," the university posted on its campus page.

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