The gunman is believed to be confined to one concrete room, and hostage negotiators are standing by.
Yountville has a population of 2,933, according to the 2010 census, with almost one-third of those residents living at the veterans home.
Kamer says his wife is now inside the home's dining hall and is not allowed to leave.
He said the hostages were employees of The Pathway Home.
Witnesses claimed the gunman entered a fundraiser party at the home, letting some people leave and taking other hostages.
Robertson says authorities have been trying to reach the gunman on his cellphone and other nearby phones.
He said authorities knew the gunman's identify but did not release it. Robertson didn't give a motive for the gunman's actions.
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A veterans facility in Yountville, California was placed on lockdown following reports of shots fired. "There were many bullets fired".
Napa County law enforcement officers were responding Friday morning to the Veterans Home of California in Yountville on a report of an active shooter in the area. "They were put into a locked down position for their own safety".
The man apparently slipped into the sprawling Veterans Home of California during a going-away party. There has been a hotline established for family members to confirm that their loved ones are safe.
"I'm waiting for a phone call from my daughter", Harrison said. "We're in lockdown in the MSC Building".
Police, SWAT teams, Federal Bureau of Investigation and agents from the Department of Alcohol, Tobacco and Firearm (ATF) swarmed the grounds - as the gunman, dressed in body armor and armed with assault rifle and tactical goggles took a clinical worker, psychiatrist and executive director hostage in building G.
The Yountville Veterans Home, located in Napa Valley wine country about 50 miles northeast of San Francisco, is the largest such facility in the United States and is home to about 1,000 veterans, according to the home's website. About 1,100 veterans from World War II, the Korean War, Vietnam War, Desert Storm, and Operation Enduring Freedom/Operation Iraqi Freedom now live at the home, the.
Army veteran and resident Bob Sloan, 73, was working at the home's TV station when a co-worker came in and said he had heard four gunshots coming from the Pathway Home.