Road now open
Police were called at 5.50am on 14 January to reports of a collision, on the M5 near junction 29 southbound, between a car and a lorry.
A woman in her 20s has been taken to Derriford hospital, by air ambulance, where she remains in a critical condition.
Three other occupants of the car have been taken to RD&E hospital by land ambulance. They have sustained minor injuries.
The driver of the lorry sustained minor injuries.
The M5 was closed for around six hours whilst emergency services attended the scene. The road is now open.
Anyone with information and anyone who witnessed the incident is asked to contact police on 101 quoting log 82 14/1/19.