The highway between Tangoio Settlement Road and Aropaoanui Road, near Tangoio, reopened at 2.40pm on Tuesday, according to an update from Waka Kotahi, after being closed for just over four hours.
Emergency services, including a rescue helicopter, were called to the smash, which was reported about 10.20am.
A Hato Hone St John spokesman said one person was taken by helicopter to Hawke’s Bay Hospital and then transferred to Wellington in a critical condition.
The spokesman said another person was taken to Hawkes’s Bay Hospital by ambulance in a serious condition.
A police spokeswoman said one car had rolled and two people had been reported trapped.