The incident at 451 Beach 72nd St., near Hessler Avenue, which unfolded just before 10:50 p.m. left a dozen people trapped in the three-story building after the third floor collapsed onto the second, the FDNY said.
Police said that party-goers could be seen fleeing the house when they arrived.
Firefighters from Ladder 121 pulled eight people from the building using a tower ladder, a spokesman said.
Four others were pulled out of the building through the front entrance.
Two people were rushed to St. John's Hospital, one in stable condition and the other in serious condition, the FDNY said.
The cause of the collapse was under the investigation. It was also not clear how many people were in the house at the time.
After the collapse, the city' Department of Buildings issued a full vacate order for the building, the FDNY said.