Masterton Fire station officer Andy Simpson said the critically injured driver had to be cut out of his vehicle before he could be taken to hospital.
"We cut the two doors (driver's side), and the 'B' pillar out of the car so we could remove him from the vehicle."
The man, in his 70s, was taken to Wairarapa Hospital by Wellington Free Ambulance, and the other driver was treated at the scene for less severe injuries.
Masterton Fire Service, Carterton Fire Brigade and police were at the scene.
The serious crash unit are investigating, and the road was closed with diversions in place from East Taratahi Rd to Hughes Line.
- Wairarapa Times-Age