A Waikato Hospital spokesperson said a man and woman were in the hospital's High Dependency Unit in serious conditions while the man transferred from Rotorua was in the Emergency Department and was still being assessed.
In a statement, Rotorua police said they would like to hear from witnesses to the crash, or anybody who saw the driving of the vehicles beforehand.
The vehicles involved were a bronze coloured Nissan Murano travelling north and two southbound cars - a white Nissan Pulsar and a dark blue Mazda Axela.
The investigation into what caused the crash is on going.
Anyone with information is asked to call Rotorua police on (07) 349 9400.
Alternatively, you can contact Crimestoppers anonymously on (0800) 555 111.