Health officials are investigating an outbreak of hepatitis A at a kindergarten in Ōāmaru.
The virus has been detected in three children from two families associated with Edna McCulloch Kindergarten.
Officials from the Southern District Health Board are working with the kindergarten to establish if any other families might be affected.
Vaccinations will also be offered to the children and staff at the centre.
Hepatitis A is a virus acquired by eating contaminated food or water and can be spread through close contact with an infected person.
Symptoms include sudden tiredness and fever, nausea and abdominal pain, followed by jaundice.
Southern DHB medical officer of health Keith Reid said officials would be carrying out blood tests next week to determine whether there were further cases.
"We are undertaking this blood testing to get a picture as to whether other families at the kindergarten might be affected, then we can offer them appropriate support and treatment. The vaccination is intended to prevent any spread of the infection," he said.
Dr Reid said it was not clear where the infection originated, but officials did not believe the kindergarten was the source of the infections.