The boat, which was being towed on Christchurch Akaroa Rd (State Highway 75) near Tai Tapu in Selwyn, caught fire about 11.40am on Thursday.
A Fire and Emergency NZ spokesman said it was a jet boat being towed by a vehicle.
A police spokeswoman said both lanes of SH75 were closed at about 11.45am and there was significant congestion around Tai Tapu. The road has been reopened.