An 18-year-old woman was killed and six others wounded in a shooting at a birthday party in California on Sunday, Antioch police said.

The shooting happened after uninvited guests showed up to a 19-year-old's birthday party at a home in the northern California city shortly before 1 a.m., the Antioch Police Department said.

Gunfire fueled panic among partygoers, who fled in multiple directions -- some of them with gunshot wounds, police said. Many victims drove themselves to local area hospitals, officials said.

The tragedy is among the latest mass shootings that killed or wounded young people at birthday parties or other ordinary events. Gunfire at an Alabama Sweet 16 party left four people dead and 28 others injured. A massacre at a Texas shopping mall left eight people dead, including several children.

Across the country, the US has suffered at least 290 mass shootings so far this year, according to the Gun Violence Archive. That's an average of more than 1.7 mass shootings every day.

The non-profit, like CNN, defines mass shootings as those in which four or more people are shot -- not including the shooter.

When police arrived at the scene of the Antioch shooting, they found a large crowd and shooting victims outside the home.

Authorities later determined a total of seven people had been shot, including the 18-year-old woman who died of her injuries at a hospital. She has not been publicly identified by police.

Other victims range in age from 18 to 20 years old, and all suffered gunshot wounds that weren't considered life threatening, police said.

It's unclear who or how many people opened fire, and whether they knew any of the victims. Police did not detail the circumstances leading up to the shooting or any possible motive.

Police said the suspect or suspects fled the area in a vehicle before officers arrived, and detectives were working to identify who was responsible. Officers were interviewing witnesses and neighbors Sunday and collecting evidence as they probe the shooting, police said.