A man lost his arm from the elbow when the car he was in ploughed into a metal fence yesterday.

But paramedics packed the arm in ice and took it to hospital with him.

The West Coast farmhand, in his 30s, was in the front passenger seat when the car went off the road near Inangahua early yesterday morning.

The scene was "gruesome", an ambulance spokeswoman said.

"It was obviously quite a nasty prang."

Neighbour D'Arcy Robinson, a former army medic, helped free the man by chopping the wire off "what was left of his arm".

"He'd basically torn his blood vessels completely. He was sort of lucid but he was in a state of shock," Robinson said.

The man and his forearm were flown to Nelson Hospital.

He immediately underwent surgery and yesterday afternoon was in a stable condition, said staff.