Six hospital wards hit by the winter vomiting bug norovirus remained shut to visitors last night.
The Royal Devon and Exeter Hospital in Exeter has seen an increase in the number of patients admitted with symptoms of the illness. But it was unable to confirm how many patients have been affected.
Staff were taking emergency measures to prevent the spread of the illness which is highly contagious.
Symptoms include sudden vomiting, diarrhoea, a temperature, headache and stomach cramps.
The bug has swept the country, leading to the closure of dozens of hospital wards. Almost 880,000 people could have been affected by the outbreak of the bug across the UK, health officials said.
The number of laboratory confirmed cases of norovirus is 83% higher than the same time last year, the Health Protection Agency (HPA) said.
A hospital spokeswoman admitted it was difficult to calculate the exact number of patients suffering from the virus because the figure were constantly changing.
She said: "In order to protect both our patients and visitors we need to restrict the number of people who visit patients.
"Please help us to achieve this by agreeing with your relatives and friends who will visit to avoid several people trying to visit the same patient at the same time and some having to be disappointed."
On many wards patients are only allowed one visitor for 30 minutes twice a day from 2.30pm-3pm and 6pm-6.30pm.
The spokeswoman added: "In exceptional circumstances, visiting outside these hours can be arranged with the nurse in charge of the ward. Please ring in advance to arrange this."
The following wards were closed: Taw, Avon, Okement, Creedy, Culm East, Culm West and Torridge.
Visitors are asked to telephone the hospital to check the status of the wards before they visit.