HALF MOON BAY, Calif. — Seven people were killed in two related shootings Monday at agricultural businesses in a Northern California community, marking the state’s third mass killing in eight days, including an attack at a dance hall that killed 11 during Lunar New Year celebrations.

Officers arrested a suspect in Monday’s shootings, 67-year-old Chunli Zhao, after they found him in his car in the parking lot of a sheriff’s substation, San Mateo County Sheriff Christina Corpus said.

Four people were found dead and a fifth injured from gunshot wounds at a farm, and officers found three other people killed at another location several miles away, the Sheriff’s Office said. Officials believe Zhao is a worker at one of the facilities and that the victims were workers as well, Corpus said. Corpus said officials hadn’t determined a motive for the shooting.

The new year has brought a shocking string of mass killings in the U.S. — six in less than three weeks, accounting for 39 deaths. Three have occurred in California since Jan. 16, according to a database compiled by The Associated Press, USA Today and Northeastern University. The database tracks every mass killing — defined as four dead not including the offender — committed in the U.S. since 2006.

The killings occurred on the outskirts of Half Moon Bay, a city about 30 miles (48 kilometers) south of San Francisco.

Half Moon Bay Vice Mayor Joaquin Jimenez said the victims included Chinese and Latino farmworkers. Some workers at one facility lived on the premises and children may have witnessed the shooting, she said. Corpus it wasn’t immediately clear how the two locations were connected.

The 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 person injured at the first scene. Shortly thereafter, officers found three more people dead from gunshot wounds at a second location nearby, Capt. Eamonn Allen said in a news release.

About two hours after first responding, a sheriff’s deputy noticed the suspect, Zhao, in his car parked outside a sheriff’s substation in a strip mall and arrested him, recognizing the car by its license plate.

A video of the arrest showed three officers approaching a parked car with drawn weapons. Zhao got out of the car, and the officers pulled him to the ground, put him in handcuffs, and led him away. A weapon was found in his vehicle, officials said. The video was captured by Kati McHugh, a Half Moon Bay resident who witnessed the arrest.

The sheriff’s department believes Zhao acted alone.

“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, home to about 12,000 people. The city and surrounding San Mateo County area is known for producing flowers as well as vegetables like brussels sprouts. The county allows cannabis farming in certain areas.

It’s a majority white community and about 5% of the population is Asian, according to Census data.

“We are sickened by today’s tragedy in Half Moon Bay,” Pine said. “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.”

On Jan. 16, a teenage mother and her baby were among six people killed in a shooting at a home in California’s Central Valley.