A road closure near the scene of the crash. Photo: RNZ
Fire and Emergency New Zealand said at least some of the injured were children.
Police said the crash happened at Hastings Rd in Matapu, South Taranaki, about 9.55am on Wednesday.
St John said four ambulances and four helicopters attended.
Two people were airlifted to Waikato Hospital in a serious condition, St John said.
Two others in a moderate condition were airlifted to Whanganui Hospital, while nine were taken by road to Hāwera and Taranaki hospitals.
Fire and Emergency NZ central shift manager Belinda Beets told the New Zealand Herald children were involved.
Hastings Rd, between Skeet and Eltham Rds, was likely to remain closed for some time while the serious crash unit investigated, police said.
