The last few riders of about 40 taking part in a cycling club road race had just crossed the bridge heading toward Martinborough and heard noises behind them.
It wasn't until the cyclists came by on the second lap of the road race that they realised a crash had occurred.
A race organiser, who did not want to be named, said by that time police, a fire crew from Carterton, Wellington Free Ambulance and the Westpac rescue helicopter were at the scene.
Skid marks on the road suggested the Prado had "weaved all over the road before rolling over", he said.
Carterton fire chief Wayne Robinson said firefighters helped ambulance officers to stabilise the man and set up a landing site for the rescue helicopter, making sure there were no overhead power lines nearby.
He said the man was lying about 60 metres from the crashed vehicle, which was on its side.
"We had a hose reel on standby in case of fire but it was not needed," Mr Robinson said.
Life Flight helicopter pilot Colin Larsen said two Wellington Free Ambulance paramedics were on board and attended to the unconscious driver before he was flown to hospital.
Yesterday afternoon the man was described by hospital authorities as being in a serious condition. No description of his injuries was given.
It is believed the driver had returned from living in Australia and had been living with family in Carterton.
Traffic Sergeant Chris McGaw said the serious crash unit had been summoned from Wellington and yesterday morning were surveying the scene and attempting to piece together the circumstances that may have led to the crash.
