Mr Smith rolled him onto his side and "he started breathing after about five seconds with all this blood and mucus in his mouth".
"It was quite shocking ... I knew he had landed quite heavily but I didn't expect him to be that bad."
Mr Smith contacted emergency service and the Otago Regional Rescue Helicopter, which was at Dunedin Hospital at the time of the incident, was dispatched to the scene.
Mr Williams, who Mr Smith said was an experienced hang glider pilot with more than two decades of flying experience, was assisted by a doctor who lived nearby, and the Waitati Volunteer Fire Brigade.
He remained in Dunedin Hospital last night for assessment, after citing neck and back pain at the scene.
"He is a lovely man, and we are glad to hear it may not be as serious as we first feared," Mr Smith said.
The crash would be investigated by a local safety officer which would go to the New Zealand Hang Gliding and Paragliding Association, which in turn would pass the report on to the Civil Aviation Authority.
Conditions were ideal for flying, "around 15-20 knots with smooth air", Mr Smith said.