Four men were shot dead and six others wounded while watching a football game in the backyard of a central California home, police said.
A gunman started shooting after entering the backyard of a south Fresno home where a gathering of family and friends was watching an American football game last night.
Police said neighbours flooded 911 dispatchers with calls for help.
The suspect fled the scene and police are searching the neighbourhood, which is about 320km north of Los Angeles, for witnesses and possible security camera footage.
"Three people died on scene," deputy Fresno police chief Michael Reed told reporters, adding that a fourth was taken to hospital in a critical condition and later died from his injuries.
All four of the dead and the six treated for "non life-threatening" gunshot wounds were men aged between 25 and 35, he said.
Others at the party may have driven themselves to hospital, police said, adding that some victims were taken to a nearby community medical centre with gunshot wounds.
Chief Reed said it was unclear how many perpetrators had been involved in the shooting and that there was "no indication" the incident was gang-related.
Police spokesman Bill Dooley said officers were looking for surveillance footage and witnesses to track the suspects.
Last night's shooting came just days after two students were shot dead at a high school near Los Angeles.
