A man was arrested on suspicion of entering West Suffolk Hospital with an imitation firearm, police have said.
Officers from Suffolk police were called to the hospital in Bury St Edmunds at 2.46am on Friday after receiving reports of a man in possession of a weapon.
The 31-year-old was arrested and an imitation firearm was seized at the Hardwick Lane site, Suffolk police said.
A police spokesman said it is not believed the weapon was held in public by the suspect or used in a threatening manner.
Police also confirmed the man was detained on suspicion of possession of a firearm or imitation firearm with intent to cause fear of violence.
He was taken to Bury St Edmunds police station, where he remains.
The hospital has confirmed the emergency department was closed for about 30 minutes following the incident.
It also confirmed that no patients, visitors or staff were harmed as a result of the incident.
Dr Ewen Cameron, chief executive for the West Suffolk NHS Foundation Trust, which runs the hospital, praised officers for their "rapid" reaction to the incident.
He said: “A security incident occurred in our emergency department at around 3am this morning, which was dealt with quickly and safely thanks to our security and emergency department teams and the rapid response of the Suffolk Constabulary.
“I would like to thank all those involved in dealing with this incident, which ensured the safety of our patients, visitors and staff.”
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