Children treated at a school dental clinic in Auckland may be at risk of Hepatitis and HIV, after a contamination scare.

A piece of equipment at Pukekohe Intermediate Dental Clinic has been broken since September 2016. But nobody realised it wasn't working until last week.

Counties Manukau District Health Board says there's a small chance children who've had some procedures have been exposed to unsterilised water, which may have had traces of blood or saliva from other children.

Parents of around 2500 children are being contacted.