Thousands of concertgoers were forced to evacuate the Lollapalooza music festival Saturday afternoon, after severe thunderstorms hit Chicago.

The festival’s performances were delayed around 3:30 p.m. and attendees were directed to take shelter in one of three underground parking garages designated to be used as an emergency evacuation shelter, reported the Los Angeles Times.

The concertgoers were allowed back into Grant Park after the storms had passed and the grounds had been searched for damage, according to the Associated Press.

Crowds were evacuated about an hour before storms arrived. The event was postponed for nearly three hours.

The lineup for Saturday’s performances was rescheduled by event organizers and the festival’s curfew was extended to 10:45 p.m. to account for the delay.