Part of the Royal Lancaster Infirmary has been shut to visitors after an outbreak of the winter vomiting bug.
At least seven patients on ward 34 have the condition, leading to its closure to the public.
Health bosses have urged people not to go to any hospital if they have suffered from, or been in contact with, someone who has had diarrhoea or experienced vomiting in the previous 48 hours - unless they have a life-threatening emergency.
A spokesman for University Hospitals of Morecambe Bay NHS Trust said visiting to the ward had been suspended, unless people had made a prior arrangement with the ward manager.
Executive chief nurse Sue Smith said: “We have confirmed the patients are affected by Norovirus – and we would ask people to follow our advice to minimise its effects on the hospital, themselves and their families.”
Norovirus is a highly-contagious bug which leaves sufferers initially feeling very unwell before they usually quickly improve as symptoms settle.
It can spread fast through hospitals, schools and care homes, and people who show symptoms such as diarrhoea and vomiting are advised to stay away from such environments.
Ms Smith added: “They should also avoid work – and only return after they have been free of diarrhoea and vomiting for at least 48 hours – during this time infectious viruses may still be present.”
The ward manager can be contacted on 01524 583434.