The party in Rochester started early Saturday as an invite-only event before it eventually grew in size after two nearby parties "infiltrated" the house. Three or four people had handguns, Capt. Frank Umbrino said.
The two people killed and 14 wounded were in their late teens to early 20s. Police responded to calls of gunshots around 12:25 a.m. and were met with 100 to 200 people attempting to flee on foot and in vehicles, he said.
Those killed did not live at the home and they were not the intended targets, Umbrino said. No suspects were in custody, and no motive was immediately known.
"A number of our young people -- babies -- that came to just hang out a little while ... left running for their lives. And that's just something that we cannot have happen," Mayor Lovely Warren said during a visit to the neighborhood Saturday.
The party's host told her she "invited a couple friends over, who invited a couple friends over who invited a couple friends over."
"And it just got out of control. She's just traumatized," Warren said.
Police were not aware of the party beforehand, and had not received any calls for disturbance, Acting Police Chief Mark Simmons said.
CNN's Jason Hanna, Christina Maxouris, Alec Snyder and Alta Spells contributed to this report.