Investigators believe a gang or drug cartel targeted the family, Tulare County sheriff Mike Boudreaux told a news conference. Deputies had conducted a drug-related search warrant at the same home recently.

Among the dead in the 3.30am shooting on Monday were a 17-year-old girl and her 10-month-old son.

“We believe the 17-year-old girl and her infant were actually running from the scene. The shooters stood over the 17-year-old mother and fired rounds into her head,” Boudreaux said. “It was deliberate, intentional and horrific.”

Also killed were a 72-year-old grandmother, two men and a woman.

Authorities had previously listed the girl’s age as 16 and her son six months old but said they had received updated information.

Sheriff’s deputies responding to reports of gunshots at the home in Goshen, a small farming town roughly 350km southeast of San Francisco, found multiple victims both inside and in the street. Three people survived the attack.

“It’s shocking for the nation, shocking to our county, shocking to our state, and I have to tell you I’m receiving phone calls from across the country,” Boudreaux said.

Police were searching for at least two suspects, Boudreaux said, but said they had not yet been identified.

The US$10,000 reward was being offered by law enforcement agencies for information that moved the investigation forward.