Hamilton police ​Sergeant David Walkley ​said the 56-year-old woman and her 21-year-old son were trapped in their Holden Astra hatchback after the accident at 7.45am on the Glenelg Highway near Muntham, about 10 kilometres west of Coleraine.

"Both were extremely lucky to have not suffered more serious injuries and that someone was travelling behind them who was able to immediately contact emergency services," he said.

"Black ice on the road caused the driver to lose control, the Holden Astra hatch rolled and came to rest on its roof."

Sergeant Walkley ​said both occupants of the vehicle were trapped.

"The young man was released from the Astra with the assistance of the Country Fire Authority road rescue crew," he said.

"The woman had to be mechanically extracted which took about an hour. Both were conveyed to the Hamilton Base Hospital but did not need to be airlifted to Melbourne."

The woman suffered serious but not life-threatening head injuries and her son moderate head and upper body injuries.

"Multiple CFA units, Ambulance Victoria paramedics and police members attended the accident scene. The Glenelg Highway was closed in both directions for about 90 minutes," Sergeant Walkley said.

"Traffic, except heavy vehicles, was able to be diverted around the accident scene. The Astra is not repairable."

Sergeant Walkley said the temperature at the accident scene was well below zero degrees.

"Drivers need to take extreme caution in those sort of driving conditions," he said.

"The highway runs through a cutting, water was leaking across the road and had frozen overnight.

“They were travelling east and sun glare was also a factor which led to the driver not being able to see the ice on the road.”