A shot has been fired into the ceiling of the Canberra Hospital after a patient stole a gun from a police officer this afternoon.

Police said the 26-year-old man was under police guard in the emergency department (ED) at about 4:00pm after being charged with a serious traffic offence earlier Wednesday morning.

The man allegedly assaulted police officers and, during the altercation, took and fired an officer's gun.

He was then subdued with a taser.

No-one else was injured in the incident and police said there was no threat to public safety.

Dane O'Donnell's wife was inside the emergency department at the time.

He said he was left wondering why the ED was shut down.

"I was a little nervous because my phone was flat, so I couldn't even call my wife to know what was going on," he said.

"I thought the worst."

ED patients urged to consider alternative treatment

Patients reported hearing the commotion from as far as the ninth floor of the hospital. ( Facebook: Bek White )

Another man, Paul Sloan, said there was "a lot of commotion" and extensive delays in the ED.

"Why there isn't a security guard in the emergency department all the time has got me beat," he said.

Patients elsewhere in the Canberra Hospital also reportedly heard the incident from as far away as the ninth floor.

Emergency department services have been impacted and some areas of the hospital have been closed, due to partial flooding caused by the shooting.

ACT Health said the ED was still operational, but encouraged people with non-life or limb threatening injuries or illnesses to consider alternative treatment.

Police refuse to comment on how patient got officer's gun

ACT Policing Acting Superintendent Marcus Boorman refused to detail how the man got hold of a police officer's weapon, saying the Australian Federal Police professional standards team would investigate the matter.

"Any incident of this nature is concerning," he said.

"We will obviously look into all of our procedures," he said.

"But it's too early to speculate and would be inappropriate to speculate. At the end of the investigation it will all be revealed."

He said the man was due to face court tomorrow for attempted robbery and a serious crash on Yamba Drive.

More charges are expected to be laid.

Level of violence staff exposed to 'unacceptable'

Canberra Hospital deputy director-general Chris Bone said patients should feel safe coming to the hospital.

But he said the level of violence staff at the emergency department were exposed to was unacceptable.

"I don't think any level of violence is acceptable in the emergency department," he said.

"Certainly the level of violence shown today is unacceptable.

"But I'm very relieved no patients and no staff were injured during the incident."