A 26-year-old man has been arrested after he entered the Royal Victoria Hospital in Belfast allegedly armed with a gun.
It is suggested the man asked a receptionist for help and then walked in to the toilets in the early hours of Wednesday morning.
A source said the man did not threaten staff.
Inspector Paul Noble said: "Police arrested a 26 year old man in the early hours of this morning, Wednesday, 18 March at a hospital on the Grosvenor Road, Belfast on suspicion of possession of a firearm in suspicious circumstances.
"He is currently in police custody."
A Belfast Hospital Trust spokeswoman said: "We can confirm that our security staff and the PSNI responded to an incident in the waiting area of the Emergency Department last night. A person was taken into custody and a firearm was recovered."