Authorities told King TV that two men were killed and another man was in critical condition after a fight in Bellevue.
The TV station reported that a woman was also injured and treated in a hospital in the suburb of eastern Seattle.
The violence appears to have occurred around 7:30 pm. The authorities said at the house heating ceremony in Elements Apartments, a three-storey complex in the city center.
The authorities told King the suspect and the victims knew each other, but they could not determine who started the stabbing or shooting.
The police will not tell the TV station if the suspect is among the deceased.
“We don’t know who did what,” police chief Steve Millett told the Seattle Times. “… we’re now going to pull the layers over to try to figure out exactly what happened.
The Times reported that Miranda Rogers, who lives in another tower in Elements Apartments, described the complex as quiet, where “something like this happens very rarely”. She added that her neighbors were always kind.
“I think this is just an unfortunate event that happened among a group of friends,” she said.