Twelve children are being treated in hospital after catching the vomiting bug E.coli at a children's farm.
Health officials said they're among 36 people so far who are believed to have caught the bug during a visit to the Godstone Farm and Playbarn in Surrey.
The children are all under 10 and four of them are said to be seriously ill. E.coli causes vomiting and diarrhoea and, in very rare cases, can be fatal.
The farm has been closed to the public while the outbreak is investigated.
Dr Angela Iversen, who's in charge of the area's health protection unit, said it was a "large outbreak" of E.coli.
"The farm owners are cooperating fully and we are working closely with them and with colleagues across health and local authorities to investigate the source," she added.
"Our advice is that the farm should remain closed to visitors while this work goes on."
A statement on the attraction's website confirmed the E.coli outbreak and said it would stay closed "until we can make sure it is quite safe for you all to visit us".