A gunman opened fire at a public transit rail yard in San Jose, California, Wednesday morning, killing at least 8 people and wounding others, Deputy Russell Davis of the Santa Clara County Sheriff's Office said.

The suspect, a male employee of the Valley Transportation Authority (VTA), is dead, Davis said. He has been identified as Sam Cassidy, a law enforcement source with knowledge of the investigation confirmed to CNN.

Police also received information about explosive devices inside the transit building, which the bomb squad is investigating, he said.

Authorities received 911 calls at about 6:34 a.m. PT saying there were shots fired near a VTA control center, a hub that stores light rail trains and a maintenance yard, Davis said. VTA employees were among the victims.

Multiple law enforcement agencies and Fire Department personnel responded to the incident using their "active shooter protocol," Davis said.

"While shots were still being fired, our teams were entering the building," Santa Clara County Sheriff Laurie Smith said.

The shooting occurred in the VTA rail yard -- not the operations control center -- at a time when light rail was starting up for the day, VTA Board Chairperson Glenn Hendricks said. The yard is where the VTA vehicles are maintained and dispatched.

"A horrible tragedy has happened today, and our thoughts and love goes out to the VTA family, the organization and what they've had to go through," Hendricks said.

There are multiple active scenes connected to the investigation into the shooting, according to San Jose Fire spokeswoman Erica Ray.

Light rail service will be suspended for the day as of noon, the VTA said, as the crime scene investigation has limited its ability to provide service. The VTA is a public transit service that operates bus and light rail services in the Santa Clara Valley and employs about 2,000 workers.

The mass shooting is the 232nd incident in which a minimum of four people were shot in the US this year, according to a tally by the Gun Violence Archive.

The Bay Area is no stranger to such spurts of violence. In July 2019, a 19-year-old gunman opened fire at the Gilroy Garlic Festival, located about 30 miles from San Jose, killing three people and wounding more than a dozen.

Agents from the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) and from the Federal Bureau of Investigation responded to the scene, and California Gov. Gavin Newsom said he was monitoring the situation.

San Jose Mayor Sam Liccardo, who also serves on the VTA board, referred to the shooting as a very dark moment for the city.

"This is a horrific day for our city, it's a tragic day for our VTA family," he said. "We know that so many are feeling deeply this loss of their loved ones and their friends."

The president of the Amalgamated Transit Union International, a labor union that represents transit workers, said the union is "shocked and deeply saddened" by the mass shooting.

"Our hearts and prayers are with our sisters, brothers, and their families at Amalgamated Transit Union (ATU) Local 265," President John A. Costa said. "We are working to provide support and assistance to the victims' families, and everyone impacted by this tragic event."

- words by Eric Levenson and Stella Chan, CNN