Some people standing on the sidelines pulled out their cellphones to record the floor collapse.
Authorities are now investigating why the floor caved in.
"You could hear the floor about to go through, kind of, but nobody thought it was going to happen".
"It was insane", Pearson said.
The multi-floor building had been leased out for a private event, Dixon said.
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Clemson University official Joe Galbraith told Greenville News that the party was hosted by the Clemson Kappa Alpha Psi student group.
Woodlands Property Management President Tal Slann told CNN that people fell through the floor into the basement.
Police said they received a 911 call at 12:30 a.m. about the cave-in and ambulances were quickly dispatched to the area. I can tell you there was a floor collapse.
According to Chief Dixon, none of the injuries appear life-threatening. "Nobody was trapped", he said.
No deaths were reported, but police said some of the injured had broken bones.
Slann sent residents of The Woodlands an email saying the floor in front of the clubhouse fireplace had collapsed during a party. "The clubhouse will be inspected by structural engineers as soon as possible".