THE headteacher of a school closed by the outbreak of a mystery illness says he has never seen anything like it in his 20-year teaching career.

Blackhall Colliery Primary School, near Peterlee, in County Durham, was forced to shut on Wednesday after a third of its pupils were struck down by a vomiting bug.

Health experts are investigating the cause but said there was no suggestion of food poisoning, as victims were not exhibiting all the symptoms of eating something contaminated.

They believe the outbreak is probably due to winter vomiting virus, a common bug that can spread quickly.

Matt Younger, who has been headteacher at the 317-pupil school for three-and-a-half years, said yesterday: "I have not seen anything like this in my entire career. I certainly hope it is the last time anything like this happens.

"We started off with one child who was sick on Tuesday afternoon and on Wednesday morning we had 73 pupils off sick before school and we realised before the registers came in that we had a big problem.

"We had another 30 children fall ill along with two administration staff, the caretaker and one teacher. We thought the best idea was to close the school.''

Mr Younger said cleaners were disinfecting the school as a precaution to ensure that there was nothing in the environment that might have contributed to the outbreak.

He said: "Coincidentally, this was the week we had our environmental standards inspection and we came out with flying colours.''

Dr Deborah Wilson, of the Health Protection Agency, said: "We know that approximately 100 people at the school have been affected by this vomiting illness, which is likely to be caused by a relatively common viral infection sometimes known as winter vomiting.

"Fortunately, the symptoms are short-lived and people recover quickly within 48 hours."

The school plans to re-open on Monday and parents have been advised to keep their children away until they have been clear of symptoms for two days in order to prevent the virus spreading any further.

Dr Wilson added: "As we normally recommend with any kind of sickness and diarrhoea, people with symptoms should ensure that they drink plenty of fluids.

"It is also important to prevent infection spreading within the home by being extra careful about hand washing and cleaning bathrooms and toilets, especially taps, toilet handles and door knobs.

"If symptoms persist, or become, severe advice should be sought from their local GP or NHS Direct on 0845 46 47."