A seriously injured person was trapped inside a truck which crashed in Featherston, South Wairarapa, just before 4pm.
Emergency services were called to Western Lake Rd, and were still working to free the person at 5pm.
The light truck, with two people inside, was the only vehicle involved in the crash.
Wellington Free Ambulance paramedics treated one person with moderate injuries, with a spokesperson saying the second, trapped occupant was in a serious condition.
Police, firefighters from Featherston and Greytown, and the Wespac Life Flight rescue helicopter were also called to the scene.
A police media spokesperson said one patient has been flown to Wellington Hospital.