Four elderly occupants were left shaken but uninjured after a runaway driveshaft crashed into their vehicle on State Highway 1 near Balclutha on Tuesday night.
Emergency services were called to Kaihiku after a tractor towing a silage machine lost its driveshaft at 6pm, Senior Sergeant Richard Whitmore said.
The driveshaft hit a 4WD Toyota coming in the opposite direction. The four elderly occupants were "shaken but uninjured".
Their vehicle was moderately damaged. Without a driveshaft, the tractor had no brakes.
However, the driver was fortunately able to coast it down a hill before coming to a stop, Snr Sgt Whitmore said.
Inquiries into the incident were continuing.