The man accused of killing seven fellow farmworkers in California told a US reporter Thursday that he was guilty and said he believes he is suffering from mental illness.

Zhao Chunli said he had endured years of bullying and overwork, but his complaints were never addressed, NBC Bay Area's Janelle Wang reported.

Wang visited the suspect in jail and was able to speak to him for around 15 minutes in Mandarin.

She told viewers she had identified herself as a journalist and told Zhao he was free to choose to speak to her or not.

"He described to me that he believes that he suffers from some sort of mental illness," she said.

"He's struggled with that for a while and he says on Monday he was not in his right mind."

Regret

Zhao, 66, was arrested hours after seven people were shot dead on the farms where they worked in Half Moon Bay, south of San Francisco.

Five have been identified as Chinese citizens, and the two others as Mexican. A Mexican man who survived the attack was being treated at a local hospital.

"He admitted that he did do it," Wang reported. "He regrets it."

She added that Zhao said he "felt that he had undergone years of bullying."

"He had lots of concerns -- long work hours -- and he brought those up and he says those were not addressed."

California officials have begun an inquiry into working conditions at the two farms in the wake of the attacks.

Governor Gavin Newsom on Tuesday said some farmworkers were "living in shipping containers" and working for far less than minimum wage.

Zhao told the journalist he was living in Half Moon Bay with his wife. He said he has a 40-year-old daughter who lives in China.

He said he had been in the United States for about 11 years and was on a green card -- a permit that allows foreigners to live and work in the country.

Wang said the suspect -- who could face the death penalty if convicted -- appeared confused about the process, and had no one in the jail to whom he could speak in Mandarin.

"I don't know if he can -- has really comprehended what's ahead of him and what he faces," the reporter said.

Zhao made a brief appearance in court in Redwood City on Wednesday.

He made no plea, and an arraignment hearing was set for February 16.

Monterey Park motive still unclear

The Half Moon Bay attack came less than two days after another deadly rampage in California in which an elderly Asian gunman killed 11 people at a dance club in Monterey Park.

Huu Can Tran, who police said was of Vietnamese origin, but had lived in Hong Kong previously, shot himself dead the following morning as police moved in.

US Vice President Kamala Harris visited Monterey Park on Wednesday, where she met with families of the victims and called for action on gun control.

"We must... require that leaders in our nation who have the ability and the power and the responsibility to do something, that they act," she said.

A vigil -- the third in three nights -- was held Wednesday outside the Star Ballroom Dance Studio.

The two horrific episodes, both involving semi-automatic weapons, sparked bafflement from California's large Asian American community, as people struggled to come to terms with what had happened.

Los Angeles County Sheriff Robert Luna admitted Wednesday his officers were still no closer to finding out why Tran had committed mass murder at the dance hall he once frequented.

Luna displayed pictures of the semi automatic gun Tran had used in his killing spree -- a Cobray CM11-9 -- a weapon that is illegal in California.

Nevertheless, "it was purchased by the suspect... in the city of Monterey Park," Luna said.

© Agence France-Presse