SAN JOSÉ: A public transit worker shot dead eight people at a California rail yard Wednesday before turning his gun on himself as police arrived, officials said, in the latest mass shooting to hit the United States.

Multiple victims were also wounded in the attack at the train maintenance compound in San Jose, just south of San Francisco, which has once again shone a spotlight on the country's raging gun control debate.

"What the hell is wrong with us, and when are we going to come to grips with this?" said California Governor Gavin Newsom at a press conference, where he praised the swift response of law enforcement.

Law enforcement officers had rushed to investigate multiple early morning 911 calls reporting gunshots, and entered the compound during an "active shooting," said Russell Davis, a Santa Clara County Sheriff's deputy.

They did not exchange gunfire with the shooter, who died from a self-inflicted gunshot wound.

"I know for sure that when the suspect knew that law enforcement was there he took his own life," said Santa Clara County Sheriff Laurie Smith. "Our deputies were right there at that time."

Bomb squads were deployed after dogs detected "some type of explosives material at the crime scene," Davis said.

US President Joe Biden called the incident a "horrific tragedy" and ordered flags to be flown at half-staff, saying in a statement: "There are at least eight families who will never be whole again."

"Once again, I urge Congress to take immediate action and heed the call of the American people, including the vast majority of gun owners, to help end this epidemic of gun violence in America.

"Every life that is taken by a bullet pierces the soul of our nation. We can, and we must, do more."