Two HGV drivers have been injured in a crash involving four lorries which closed a section of the M1.
The drivers were both taken to Queen's Medical Centre in Nottingham following the accident between junction 25 and 26, just north of Trowell services on the northbound carriageway in the early hours.
One driver is said to be in a serious condition, while the other was treated for non-life-threatening injuries.
A third driver was treated at the scene.
Police are investigating the crash and one line of inquiry is that a small red car with a faulty rear light might have caused a HGV to brake suddenly, leading to the collision involving four lorries, a police spokesman said.
There was dense fog at the time of the crash and visibility was poor.
Rush-hour commuters were advised to avoid the area and the northbound carriageway remained closed while police carried out inquiries at the scene.
The section was expected to be reopened later this afternoon.
The southbound carriageway was unaffected.
Drivers on the motorway at the time of the incident, between 3.10am and 3.20am, were asked to contact the police to help with the investigation.
The stretch of motorway has been reopened, police said.