The shooting took place just several days after another shooting attack in California killed 11 people at a dance hall.

At a news conference on Tuesday, San Mateo County Sheriff’s spokesperson Eamonn Allen told reporters that evidence suggested that the attack, which took place on Monday night in the area of Half Moon Bay, was carried out with a legally purchased semi-automatic handgun.

“All the evidence we have right now points to a workplace violence incident,” said Allen, adding that the victims were “all adults, seven males one female, and a mixture of Asian and Hispanic victims”.

San Mateo County Sheriff Christina Corpus said that the wounded victim at the hospital was out of surgery and “stable”.

The shooting has brought new anguish to the small community, surrounded by coastal farmland and home to many migrants who work in the region’s agricultural sector.

Half Moon Bay Vice Mayor Joaquin Jimenez said the victims of Monday’s attack included Chinese and Latino farmworkers. Some workers lived at one of the facilities and children may have witnessed the shooting, she said.

The attack came as California was still reeling from a shooting at a southern California dance hall that killed 11 on Saturday night.

The suspected attacker in Monday’s incident, a 66-year-old Half Moon Bay resident named Chunli Zhao, was detained later that day.

Allen said that Zhao did not actively surrender to law enforcement, but was identified by a deputy by the make of the suspect’s car in the parking lot of the Half Moon Bay substation. After being given commands, he got out of the vehicle and was detained “without incident”.

Zhao was employed at a mushroom farm in the area, and Allen did not elaborate on what, if any, criminal history he may have had. However, Allen said that there were no “specific indicators that would have led us to believe that he was capable of something like this”.

“The only known connection between the victims and the suspect is that they may have been coworkers,” said Corpus.

Allen noted that a series of storms that brought flooding and extreme weather to the area had put many in the community under pressure.

“There’s been flooding, there’s been people out of work, so the coast has certainly had its share of challenges recently,” he said.

Corpus told reporters that identification of the victims and notification of next of kin was continuing, a process complicated by the fact that some victims were members of the area’s migrant community.

Half Moon Bay is a small coastal city with agricultural roots, home to about 12,000 people, about 50 kilometres (30 miles) south of San Francisco. The surrounding San Mateo County is a mixture of coastal cities and hills dotted with farms, including floral and tree nurseries, as well as ranches.

District Attorney Steve Wagstaffe told reporters on Tuesday that Zhao’s arraignment would take place at 1:30pm (21:30 GMT) on Wednesday.

“The charges have not yet been determined,” he said. “The charges obviously involve the homicides involved.”

Wagstaffe added that “we’ve never had one [a case] in this county, of this many deaths … at one time.”