In the second instance of mass shooting in four days, seven people were killed on Monday in Half Moon Bay near San Francisco in US state of California.?

The suspect is in police custory. He has been identified as 67-year-old Chunli Zhao.?

Officials said that seven people were killed in two related shooting incidents in Half Moon Bay, a city 48 kms south of San Francisco. Four people were killed at a farm and three were killed at the trucking business on the outskirts of Half Moon Bay.?

San Mateo County Board of Supervisors President Dave Pine said Zhao, the suspect in custody, worked for one of the businesses and was a "disgruntled worker".

The San Mateo County Sheriff's Office first received reports of a shooting just before 2:30 p.m. and found four people dead from gunshot wounds and a fifth injured person at the first scene. Shortly thereafter, officers found three more people dead from gunshot wounds at a second location about five miles (8 kilometers) away, said Capt. Eamonn Allen in a news release.?

About two hours after first responding, a sheriff's deputy found the suspect, Zhao, in his car at a sheriff's station in Half Moon Bay. He was taken into custody and a weapon was found in his vehicle. The sheriff's department believes he acted alone, Allen said.?

The office did not share any information about the connection between the two locations.

The motive for the shooting is not known, Allen said.

“We're still trying to understand exactly what happened and why, but it's just incredibly, incredibly tragic,” said state Sen. Josh Becker, who represents the area and called it “a very close-knit” agricultural community.

Aerial television images showed police officers collecting evidence from a farm with dozens of greenhouses.

Half Moon Bay is a small coastal city with agricultural roots now home to about 12,000 people. The city and surrounding San Mateo County area is known for producing flowers as well as vegetables like brussell sprouts. The county allows cannabis farming in certain areas. It's a majority white community and about 5 per cent of the population is Asian, according to Census data.?

Pine said, "We are sickened by today's tragedy in Half Moon Bay. We have not even had time to grieve for those lost in the terrible shooting in Monterey Park. Gun violence must stop."

California Gov. Gavin Newsom tweeted that he was "at the hospital meeting with victims of a mass shooting when I get pulled away to be briefed about another shooting. This time in Half Moon Bay. Tragedy upon tragedy."

The shooting was the sixth US mass shooting this year — and followed the killing of 11 people late Saturday at a ballroom dance hall in Southern California.

In yet another shooting, two students were killed in ?Des Moines in Iowa state. However, it would not be classified as a mass shooting as the US Department of Justice says a mass shooting is one in which four or more people are killed.?

(With AP inputs)