Both driver and firefighter ended up in Dunedin Hospital with moderate injuries following the 2.45am incident.
Police said the heavy motor vehicle swerved off State Highway 1, about 500m north of Mile Flat Rd, near Hampden, when the 49-year-old driver allegedly attempted to avoid an animal on the road.
It travelled about 50m in a ditch beside the south-bound lane, before hitting a power pole, which broke in half, and uprooting a fence post.
The vehicle came to a halt about 3m from a steep 7m drop to the railway line.‘‘She (the driver) was a very lucky lady,'' a police spokeswoman said.
The injuries to the driver's legs and abdomen were not believed to be serious, but she was taken by ambulance to Dunedin Hospital.
She was cut free from the vehicle by volunteers from the Weston and Palmerston brigades.
While cutting the woman out of the truck, one of the Weston firefighters fell 4m to 7m to the railway line below.
‘‘They cut the door [of the truck] off and he stepped back with the door and went down the bank,'' a spokeswoman said.
The firefighter injured his back and he was taken to Dunedin Hospital, she said.
When contacted, Weston chief fire officer Bevan Koppert declined to comment on the exact nature of the incident as it was being investigated.
The cause of the crash is also being investigated.
The truck was being driven by a vendor contracted to Coupland's Bakeries.
No-one from the company was able to comment on the crash or the state of the driver yesterday.
