Twelve children have been affected by an outbreak of E-coli in the Lurgan area, the Public Health Agency has confirmed.
An industrial cleaning operation is underway at Holly House Day nursery in Dollingstown.
It has closed voluntarily until further notice as an investigation into the source of the outbreak is carried out.
The Public Health Agency has said it is investigating but none of the children are seriously ill.
Dr Neil Irvine, Consultant in Health Protection at the Public Health Agency said: "The nursery has decided to close voluntarily and has been advised of all relevant measures to take in the management of this situation.
"All appropriate infection control measures are being taken and the nursery is co-operating fully with the PHA.
"Parents of children who attend the nursery have been contacted to advise them of the situation and what they should do. Parents are encouraged to contact their GP if their child develops a diarrhoeal illness."
A spokesperson for Holly House Nursery said that their concern is for all the children in the care, their families and nursery staff.
"Public Health tests on food at the nursery have been clear and we are relieved that the investigation has found no evidence to suggest that the source of the infection is the nursery itself.
"We greatly appreciate the response of parents which has been overwhelmingly supportive. We are now working towards the re-opening of the nursery which we expect to be during the course of this week."
SDLP Craigavon Councillor Mary McAlinden has wished the nursery school children affected a full and fast recovery.
"This is a very worrying time for the parents of these young children who are suspected to have contracted E-coli poisoning.
"I appeal to people to exercise caution when preparing meals and to ensure that food is properly refrigerated and cooked thoroughly before being eaten.
"I also urge parents in the area to seek medical attention immediately if their child displays any symptoms of E-coli poisoning and wish the toddlers affected a full and speedy recovery."
© UTV News