Roof collapses under partying university students

A partygoer has captured the moment 30 US college students plunged over a storey after the garage roof they were standing on collapsed.

An estimated 1000 Cal Poly University undergraduates watched on as the structure at off-campus housing in San Luis Obispo, California buckled under the group's combined weight, injuring eight and sending four to hospital early Saturday morning.

Only one student was seriously injured, with a "large wood splinter" in her leg.

In a video obtained by the school's newspaper Mustang News gasps rang out from the crowd, many of whom were perched on adjacent roofs and in trees.

While those left still standing on the caved structure scurried to safer ground.

According to KNBC, the group of 30 had scaled the roof during St Patrick's Day celebrations although their motivation remains unclear.

More than 1000 students are said to have attended the party, which was part of the 20,000-strong university's unofficial "St Fratty's Day" festivities.