SANTA CLARA, May 26 (Reuters) - A California transit employee killed eight co-workers and wounded another before taking his own life on Wednesday,the latest in a spate of deadly U.S. mass shootings, prompting the state’s governor to ask: “What the hell is wrong with us?”

Authorities did not immediately offer many details or a possible motive for the shooting, which unfolded about 6:30 a.m. Pacific Time (1330 GMT) at a light-rail yard for commuter trains of the Santa Clara Valley Transportation Authority (VTA), in the heart of Silicon Valley in the San Francisco Bay Area.

A bomb squad was searching the yard and adjacent buildings after at least one explosive device was found, Santa Clara County Sheriff's Deputy Russell Davis said at a news conference.

Sheriff Laurie Smith told reporters that gunfire was still going on when her first deputies arrived on the scene, and that the assailant took his own life, apparently when he became aware that police were closing in on him.

Officers never exchanged gunfire with the suspect, Davis said. Still, Smith credited swift action by sheriff's deputies, who rushed to the scene from their own headquarters next door to the rail yard, preventing what might have been a much greater loss of life.

Governor Gavin Newsom, appearing with Smith and others in San Jose, voiced exasperation at the frequency and regularity of gun violence in America.

"There is a sameness to this and that numbness, I think, is something that we are all feeling," Newsom said. "It begs the damn question, What the hell is going on in the United States of America? What the hell is wrong with us and when are we going to come to grips with this?"

The gunman, the eight victims shot dead, and a survivor who was hospitalized in critical condition were all employees of the transit agency situated near the city's airport, officials said. The victims were found in two buildings on the site.

Authorities did not release the gunman's name or age. The San Jose Mercury News and other media outlets identified him as Samuel Cassidy, 57, a maintenance worker at the yard.

Cassidy had worked for the transit authority since at least 2012, when he was listed as an "electro-mechanic," and was promoted to "substation maintainer" in 2015, according to records posted by the nonprofit website Transportation California.

Last year, he earned a salary of $102,000, plus benefits and $20,000 in overtime, the records showed.

The suspect and another individual filed domestic violence restraining orders against one another in 2009, three years after Cassidy divorced his spouse, according to online court records.