Launceston General Hospital has been closed following the discovery of a potentially lethal bacteria that causes Legionnaire's Disease.
Patients are being moved to other hospitals after legionella was found during "routine water quality surveillance".
The hospiotal is expected to be closed for four weeks, however there are no reports of anyone becoming infected.
Peninsula Community Healthsaid: "On Friday, February 15, as part of our routine water quality surveillance, we were made aware that legionella bacteria was present in two locations at Launceston General Hospital.
"This posed a minimal risk to patients and staff and immediate action was taken to ensure patient and staff safety in line with our risk management strategy and legionella policy. There has not been any breach of local policy or legal duties and obligations.
"To allow a robust disinfection of the water system and a major refurbishment of the heating and water system we have taken the decision temporarily close Launceston Hospital for four weeks. This will allow planned maintenance to the plumbing and heating system costing over £100,000, followed by the disinfection the whole system using a high concentration of chlorine which will be flushed through the whole water system.
"The hospital will reopen once this work is complete and we have a confirmed clear water quality reading following further testing ensuring ongoing patient and staff safety.
Chief Executive Kevin Baber said: "I would like to reassure patients and staff that we have taken this decisive action to ensure public safety. Whilst we acknowledge the short term disruption, we are confident that closing Launceston General Hospital for a short period of time will allow us to resolve the situation going forwards. I would like to thank the patients, families and staff involved for their cooperation and support."
The Launceston Minor Injuries Unit (MIU) will be closed from 5pm today (Monday 18 February 2013) and patients are advised to attend alternative MIUs at Liskeard and Stratton Community Hospitals.
Carol Williams, director of nursing for the primary care trust, said: "Our immediate priority is to support Peninsula Community Health in the safe transfer of the small number of in-patients at Launceston in to other appropriate care setting where their needs can continue to be met. Staff have talked with families and patients and we will are working with Peninsula Community Health to ensure they have taken all possible measures to ensure public safety.
"Remedial work will be starting imminently and we will support the reopening of Launceston Hospital once this is complete and it is safe to do so."