An 18-year-old woman was killed and six others were wounded in a shooting at a birthday party in Antioch, California, early Sunday morning, 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 am, the Antioch Police Department said in a news release.

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

Police received multiple 911 calls reporting gunfire at the home and arrived to find multiple shooting victims outside and a large crowd, the department said.

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 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, according to police.

It's unclear who or how many people opened fire, and whether they knew any of the victims. Police did not provide details on 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 still working to identify who was responsible. Detectives were interviewing numerous witnesses and neighbors Sunday and collecting evidence as they probe the shooting, police said.