"We just went down there and found the car upside down," he said. "She was conscious. She said, get me out of here."
Emergency services were "extremely fast" in their response, arriving about 15 minutes after being called.
When Hawke's Bay Today arrived at the scene, three fire crews were working in the rain to cut the woman from her vehicle.
Hastings senior station officer Michael Manning said it took about 30 minutes to rescue the woman. She was conscious throughout, but "in a lot of pain".
The fire crews exercised extra caution with the jaws of life, after ambulance officers told them the woman had possible neck and spinal injuries.
"She was quite badly trapped by her legs. It was a very careful and methodical process," he said.
A team of five people carried her on a stretcher to the Lowe Corporation Rescue Helicopter, which landed in a nearby paddock.
She was airlifted to Hawke's Bay Hospital, where she was in a critical condition last night, a hospital spokeswoman said.
Mr de Munk said this was the second time a car had careened off the bank into his property.
He said that 10 years ago, a car full of young people came off the same bank and became trapped in some berry bushes, but they did not receive serious injuries.
Meanwhile, in Elsthorpe, a man managed to walk 5km to a phone after the vehicle he crashed caught fire.
The 38-year-old man rolled his vehicle into a ditch sometime during the evening.
He managed to free himself and walk 5km to a house to raise the alarm.
The Lowe Corp Rescue Helicopter crew responded to the call at about 7.30am yesterday morning. The man was airlifted to Hawke's Bay Hospital for further treatment and later discharged.
