"They were shearers. It was a flat piece of land. They were obviously racing when they hit a bump and tipped over," Mr Jackson said.
It is not known if the injured woman was wearing a helmet.
So far this year, eight people nationwide have died in agricultural workplace accidents, a rate which is almost two-and-a-half times the average across all industries.
Tim Wilson of Just-Ice consultants in Martinborough, which specialises in agricultural health and safety, said he believes much more needs to be done to improve health and safety procedures and the opportunity exists to do something about it..
In agreement is David Calvert, chief executive of the NZ Safety Council.
Mr Calvert said the innocence and freedom associated with rural life can lead to complacency.
"Someone needs to draw a line in the sand," he said. "Quad bikes and tractors frequently roll over. Some parents will say their children are brought up to ride them, but you should be 16 and there should always be rollbars and helmets. You wouldn't ride a motorcycle without a helmet."
New Zealand's workplace health and safety record is poor when compared to countries such as Australia and Britain, and the agriculture sector is one of the worst offenders.
Mr Calvert said a lack of training across all sectors, a lack of political leadership, fragmentation of resources and a lack of imagination are hindering the implementation of health and safety.
"The Department of Labour has a whole lot of people with the effectiveness of feather dusters," he said. "We have politicians with backgrounds in law and political science ... a lot of these people don't have the technical skills to recognise the changes that are required. There's no engineers."
