Williamson was hurt following an incident near the finish of a race at Alexandra Park in Auckland last night.
He was driving Captains Mistress when he was unseated from his cart close to the winning post and fell on to the track, Harness Racing New Zealand reported.
Williamson received immediate medical attention on course before being transported to hospital, where he remains under care.
Harness racing broadcaster Greg O'Connor said Williamson had been placed in a coma, which was normal protocol with a serious head injury.
Williamson grew up in North Otago and, with parents Phil and Bev and brothers Matt and Brad, has had a long association with harness racing.
HRNZ chief executive Brad Steele said the sport’s thoughts were with Williamson, his wife Katie, their family, and all those affected. — Allied Media
