Several students who were partying at an early St. Patrick’s Day party  Saturday were hospitalized after a garage roof collapsed beneath them. Fewer than 10 students attending the “St. Fratty’s Day” party were injured in the incident, said a statement issued by California Polytechnic State University, which is near the neighborhood of student rental houses where the party took place.

The off-campus party was part of a weekend celebration attended by several thousand students. Local police began receiving complaints Friday night into Saturday about the disturbance, and showed up to start issuing citations for noise violations and underage drinking.

Around 6 a.m. PST, about 30 people were standing on the roof of the garage when it collapsed, the San Luis Obispo Police said. Four people were taken to the hospital and two had moderate but not life-threatening injuries, the statement by Cal Poly said. All other injuries reported as a result of the incident were minor.

Matt Lazier, spokesman for Cal Poly, told the Associated Press sororities and fraternities at the school had been on probation since the start of the year due to allegations of sexual assault and were not supposed to host any parties. Lazier warned that the school would investigate the role of any Greek Life organizations in Saturday’s incident and punish them accordingly.

Police Capt. Chris Staley told the Tribune of San Luis Obispo his force was also caught off guard by the celebration, which some students said was moved up a week to avoid the double fines his department imposes on revelers on official holidays. The event was largely organized by students on social media.