Most power was restored to UC Berkeley overnight after a powerful explosion Monday evening left four people with minor burns and caused the campus to go dark.

Some power was restored to the campus as of 11:15 p.m., and university officials were slated to give an update on the situation Tuesday morning.

The blast and fire north of California Hall, which forced students to scramble for safety and sent a dark cloud of smoke into the air, was probably caused by the theft of copper wire from an off-campus electrical station, a UC Berkeley spokesman said.

One of the victims was taken to a hospital; the others declined to be transported, officials said About 20 people were rescued after being trapped in elevators.

Officials asked that the public stay away from the main campus until power is fully restored to the campus, although residence halls had been cleared for students to return, according to an incident update from the university.

The blast was reported about 6:30 p.m., about two hours after a power system failure, UC Berkeley spokesman Dan Mogulof said.

He said the stolen copper wire was discovered last week and repaired Sunday.

"We have a strong suspicion that what happened is related to vandalism discovered last week," Mogulof told reporters. "The damage they caused may have been far more extensive than we originally thought."

He said the blast area was two stories high and two roadway lanes wide and sent at least one manhole cover shooting into the air. Ripping the wire out of the system required a lot of force and probably special equipment, Mogulof said. The explosion took place as engineers were attempting to bring power back up, he said.

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lee.romney@latimes.com

robin.abcarian@latimes.com

Times staff writer Robert J. Lopez contributed to this report.