Four members of a California family who were kidnapped at gunpoint earlier this week, including an eight-month-old infant, have been found dead.

Aroohi Dheri, her mother Jasleen Kaur, 27, her father Jasdeep Singh, 36, and Dheri's uncle Amandeep Singh, 39, were identified as the victims.

A farmhand working in an orchard in rural Merced County, California, discovered their bodies.

"A whole family was wiped out, and we have no idea why," Merced County Sheriff Vern Warnke said at a news conference on Wednesday evening.

A suspect has been detained by police, but no motive has been identified.

Warnke did not say how the family was killed, but he did say they were most likely murdered before they were reported missing.

Surveillance video released on Wednesday shows a man holding what appears to be a firearm talking to the male victims outside their trucking company in Merced.

The victims are then loaded into a pickup truck, hands zip-tied behind their backs, and the suspect drives away.

When the truck returns a few minutes later, the suspect enters the property and walks Kaur and her infant to the truck, gun in hand.

Jesus Manuel Salgado, 48, was arrested on Tuesday after his family contacted police and told them he had admitted to being involved in the kidnapping.