Law enforcement authorities from multiple agencies responded to a report in the morning of shots being fired at the Yountville Veterans Home in Napa County, working to clear buildings and establish a perimeter.
A sheriff’s deputy exchanged gunfire with the assailant, a California Highway Patrol spokesman said. The suspect released some people before retreating into a room with three hostages, all of whom were employees of a programme called the Pathway Home that works with veterans of the conflicts in Iraq and Afghanistan.
There were no reported injuries. In the early evening, California Highway Patrol spokesman Sgt Robert Nacke said he knows of no contact on Friday with the gunman or the people who were holed up with him at the veterans home.
“There has not been any confirmed communication with the gunman since 10:30 in the morning,” he told reporters.
Calling the situation at the veterans home “dynamic and active”, Mr Nacke said he had no information about the hostages or their conditions.
Police tactical teams are forming plans on how to deal with the ongoing situation, he added.
“We have quite a few hostage negotiators working for a peaceful resolution to this”, Napa Sheriff John Robertson told reporters in the afternoon, adding that he did not yet know what the suspect’s potential motivation was.
Authorities said they had identified the shooter but were not yet releasing his name. They said he was believed to have used a rifle but did not identify the model.
A man named Larry Kamer, who said his wife worked as fundraiser for Pathway Home, told multiple news outlets that the gunman entered a going-away party before seizing hostages.
Napa County Sheriff’s officials directed people to avoid the area. The California Highway Patrol said it had deployed officers and a SWAT team to the scene.
Video from the scene showed an armoured vehicle joining police cars in surrounding the facility.
The facility is America’s largest veteran’s home, according to California, housing some 1,000 people.
Yountville sits in the heart of California wine country, an area known for fine wine and upscale restaurants.