Six children aged between eight and 16 were taken to Wairarapa Hospital after an inflatable slide collapsed at the Masterton A & P Show today.
Emergency services were called to the Solway Showgrounds about 1pm.
A spokesperson for St John Ambulance said the children suffered minor and moderate injuries.
Five children have since been discharged from hospital, but an 11-year-old may spend the night for observation following a potential knock to the head.
In a statement, the Masterton A & P Association said the slide was immediately closed to the public following the incident on the mammoth slide, and police and Worksafe were now investigating.
"The Masterton A & P Association is very concerned about the welfare of the children and are thinking of the families involved," the statement said.
"However until the investigation has been completed, we are unable to make further comment."