The University of California, Berkeley, has been evacuated after an explosion occurred as a result of a campuswide power outage.

According to the university, an explosion occurred as a result of a “power system failure” that began affecting the campus around 4:45 p.m. PDT. The Berkeley campus lost power from Strawberry Canyon to University Hall, as buildings including University House, the chancellor’s residence, units 1, 2 and 3, Maximino Martinez Commons and Foothill were all reported affected.

Some 90 minutes later, an explosion occurred on campus, though the exact location remains unknown. Berkeley Fire Department Chief Gil Dong tells the Daily Californian that the explosion may have originated at an underground electrical vault near Bancroft Library. He also added that multiple emergency vehicles were already on the scene.

Soon after the explosion, around 6 p.m. PDT, Berkeley officials sent out an emergency message to all students and staff canceling classes for the day and advising everyone to leave the campus as quickly as possible.

“The power outage and explosion were due to a power system failure. All are asked to leave the main campus area immediately,” Berkeley officials wrote in an emergency announcement. “The main Berkeley website is experiencing difficulties due to a power outage on campus. Classes are canceled and labs are closed.”

Currently, there is no word on what caused the UC Berkeley fire, though Christine Shaff, communications director for Facilities Services, tells the Daily Californian that the power outage and resulting explosion could have been caused by vandals attempting to strip copper from the university’s high-voltage power system.

She also added that some students and faculty are still stuck inside campus buildings, and that rescue crews are currently at work attempting to free them.

“We do know there are some people are stuck,” she said. “That’s one of our top priorities.”

Watch an eyewitness video of the UC Berkeley explosion below.