Police in Rotorua believe some of the teenagers involved in a van crash on Saturday may not have been wearing seatbelts.
The group of 12 friends was travelling back from a party in Taupo, police say, when their van failed to take a left-hand bend, crossed the centre line and hit a bank on State Highway 5 just south of Rotorua, about 2.45am.
Officers arriving at the scene found bodies of injured lying on the road and in ditches, having apparently been thrown from the vehicle when it flipped onto its side.
Senior Sergeant Brent Crowe says officers found a couch in the back of the van, which is leading police to question whether anyone was properly secured.
Three 17-year-olds were transferred from Rotorua to Waikato Hospital's intensive care and high dependency units on Saturday and a 16-year-old was transferred to Waikato on Sunday.
Four teenagers remain in Rotorua Hospital wards, all in a stable condition, two have now been discharged and it's expected another two who were involved in the crash will be discharged from Rotorua Hospital later on Sunday.
The group included students of John Paul College in Rotorua.