The pilot was spreading fertiliser on Mt Linton Station, near Ohai, when his Phoenix Aviation plane crashed just before 1pm.
Tom Anderson, who works at the station and is also a volunteer for the Ohai fire brigade, pulled the pilot from the wreckage, chief fire officer John Hogg said.
''He was Johnny on the spot.''
The pilot - a 43-year-old Gore man - was ''dazed and confused'' following the impact, which forced the engine some 20m away.
''As time went, the pilot got in more pain. From what we could see he had serious abdominal and internal injuries.''
He was taken by Southern Helicopters to Southland Hospital, and remains in a serious condition.
Mr Hogg said at first it was feared a fuel leak mixing with the fertiliser could be dangerous, but later it was found ''there was no danger for us''.
Mt Linton Station general manager Ceri Lewis said ''it is good the guy is alive ... he is bloody lucky''.
Civil Aviation Authority would be at the scene today to investigate the cause of the crash, police said.
