The driver of the green car died at the scene and the teen was flown to Waikato Hospital.
In the second crash, on State Highway 25a, a car carrying parents and a teenage son and daughter careened down a bank on Kopu-Hikuai Rd, between Kirikiri Valley and Puketui roads.
The Trustpower TECT Rescue Helicopter, based in Taupo, and the Northland Emergency Services Trust helicopter, flew patients to hospital.
The mother is stable in a ward and her 14-year-old son, who received multiple injuries, is in a critical condition in the intensive care unit.
The father was last night discharged from hospital and a teenage daughter remains in Thames Hospital with moderate injuries.
The Tairua Volunteer Fire Brigade was one of several brigades to attend the crashes. In a Facebook post, photos of the crash show how the conditions emergency services had to deal with to free those involved.
"First pic shows how lucky the occupants were that someone was behind them as they may have been missing for some time.
"Four ambos, three fire appliances and two choppers were required to get these people on the way to hospital. We wish them speedy recoveries. Drive safe people !!"
The serious crash unit is investigating.
Police reminded motorists to take care on the roads and make sure they were well rested, free of distractions and drove to the conditions.