The man was thrown from his vehicle after it came off the Tapanui-Raes Junction Highway about 6.20pm, Southern District Command Centre deployment co-ordinator Senior Sergeant Steve Aitken said.
A St John spokeswoman said the man was taken by Otago Regional Rescue Helicopter to Dunedin Hospital with serious head injuries about 7.30pm.
A Dunedin Hospital spokesman said the man was in a critical condition late last night.
After being assessed by staff in the hospital's emergency department, he was admitted to the intensive care unit.
Snr Sgt Aitken said the man was driving towards Alexandra when his vehicle came off the road.
His family had been notified of the crash.
No other vehicles were involved.
The circumstances of the crash were still being investigated, Snr Sgt Aitken said.
