She was flown to hospital by the Palmerston North Rescue Helicopter, and was last night in a critical condition in the intensive care unit.
Pilot Marc Bridgman said the woman was lucky to have survived the collision.
"The train was coming at some speed and it spilt the tractor in two. There was an instrument that was on the back of it [the tractor] and that was on one side of the train and the rest of the tractor was on the other side. It was quite a major impact."
The accident happened on a sweeping corner where it was hard to see oncoming trains, he said.
"And of course the tractor wouldn't be going very fast, so it hit her square on."
Train services were delayed while the scene was cleared.
Amelia Wade