Six people including a six-month-old baby cradled in the arms of her 17-year-old mother were shot dead at a home in California's main agricultural valley on Monday in what authorities called a targeted attack and "horrific massacre."

Tulare County Sheriff Mike Boudreaux linked the killings to the illegal drug trade, saying deputies had conducted a drug-related search warrant at the same home last week.

"We believe this was a message being sent," Boudreaux told reporters at the scene. "We believe that this was a targeted family."

Two suspects remained at large, he said.

Authorities responded early on Monday after multiple shots were heard. Some victims were found in the street while others were discovered in the house.

One victim was alive and wounded when authorities arrived but later died at a hospital, Boudreaux said.

The attacks occurred in Goshen, a farm community of 5,400 people about midway between Los Angeles and San Francisco.

The bodies of the infant and 17-year-old mother were located in a ditch outside the home, Boudreaux later told the Los Angeles Times. Both had gunshot wounds to the head.

Several others were shot in the head, including an elderly woman. Two women survived by hiding in a trailer on the property.

"I think it's specifically connected to the cartel. The level of violence ... this was not your run-of-the-mill low-end gang member," Boudreaux told the newspaper.

"If (they) are specifically shooting everyone in the head, they know what they are doing ... (and) they are comfortable with what they are doing."

The newspaper reported that last week's search warrant resulted in one arrest and the seizure of guns, marijuana and methamphetamine.