The Norovirus bug - which causes diarrhoea and vomiting - has spread to three more wards since Monday.

It is thought to have been brought in by a visitor. The wards, in different parts of the hospital, remain open to existing patients.

A spokesman for the hospital said they were trying to keep the hospital working and manage the situation.

"When a patient develops symptoms due to Norovirus, the infection is easily spread to those in close proximity, therefore standard procedure is to prevent new patients being admitted," he said.

Anyone with symptoms or the illness is being asked not to visit patients unless absolutely necessary.