"We're looking for an old type of motor vehicle that's possibly done a u-turn in front of them [the crash victims]," he said. "That driver may have been unaware that they've caused the crash."
Mr Membery said police would speak with the people in the Holden once they had received medical treatment.
Investigations were at an early stage but police hoped witnesses to the crash would come forward with a registration plate or a description of the car they were looking for.
He also hoped the driver of the vehicle which did the u-turn might realise they had caused the crash and contact police.
Anyone who saw the incident is asked to contact the Rotorua police station on (07) 348 0099 or 0800 TIP OFF.