New Hampshire Homeland Security has said the suspect is dead, all patients are safe and there is no active threat to the public, though the scene "remains active".

The Associated Press reports that, other than the suspect, one person was shot, citing an anonymous law enforcement official.

The shooting was "contained to the front lobby" of the hospital, according to the Homeland Security department, and authorities are investigating a "suspicious vehicle".

It is not clear what condition the victims are in, but New Hampshire State Police said in a statement "multiple" people have been shot.

New Hampshire Governor Chris Sununu also said the incident has been contained.

"While the scene remains active as the campus is cleared, the suspect is deceased," he said. "The state immediately mobilised, and first responders and law enforcement are on the scene."

New Hampshire Hospital, which has roughly 185 beds, is the state psychiatric hospital, located in the state's capital city, Concord.

An armoured vehicle was seen approaching the scene outside the hospital.

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New Hampshire State Police said earlier on Friday night: "Troopers are currently investigating a shooting at New Hampshire State Hospital in Concord.

"There are multiple victims. Additional updates will be released when available."

Aerial views of the hospital show an active scene with numerous police cars outside the hospital.

The shooting is the latest act of violence at a hospital in the US, with medical centres across the country struggling to adapt to growing threats.