Aaron Tung, principal at Concord Farms, one of the locations where the shooting took place, said the company wanted to thank the community for the "outpouring of thoughts and support."

"We thank law enforcement for their swift response and actions. Concord Farms is a family owned and operated mushroom farm at this location for 37 years," he said in a statement.

Tung added, "With no past knowledge with this gunman or his motives, we are shook and very eager to gain more information from the authorities and their investigations. Our hearts are with the victims, their families and the Chinese American community—from Half Moon Bay to Monterey Park."

-ABC News' Abigail Shalawylo

San Mateo County Sheriff Christina Corpus said a semi-automatic handgun was found in the suspect's car.

The suspect, 67-year-old Chunli Zhao, is cooperating and being interviewed, the sheriff said.

Zhao is believed to have acted alone, Corpus said.

-ABC News' Marilyn Heck and Abigail Shalawylo

The gun violence in the U.S. is at "completely unacceptable levels," and it "really hit home tonight," San Mateo County Board of Supervisors President Dave Pine said Monday. "Our hearts are broken."

"But in the end, there are simply too many guns in this country," Pine said. "And there has to be a change. This is not an acceptable way for modern society to live its conduct its affairs."

-ABC News' Marilyn Heck and Abigail Shalawylo

San Mateo County Sheriff Christina Corpus said the department was dispatched at 2:22 p.m. local time with reports of a shooting in unincorporated San Mateo County with multiple victims.

At the first location, four people were found dead with gunshot wounds and a fifth person was taken to the hospital and is in critical condition, Corpus said during a press briefing Monday.

Shortly afterward, three additional victims were found dead at a separate location about a mile away, the sheriff said.

Both locations are nurseries, large rural properties, and some people live on site; children witnessed the shooting, Corpus said. The victims are thought to be workers.

The suspect is thought to be a farm worker, Corpus said.

The motive and the relationship between the victims and the suspect are unknown at this time. The suspect is cooperating and being interviewed, Corpus said.

-ABC News' Marilyn Heck