The M1 remains closed in both directions between J12 and J13 at Bedfordshire following an accident involving a lorry and a car.
The driver of the lorry, which was travelling southbound, had to be cut free from his vehicle and was airlifted to hospital with a serious leg injury. The car driver, who suffered minor injuries, was also taken to hospital.
It is understood that the lorry hit the central reservation and crossed over onto the northbound carriageway just after 12.30pm today.
Police are still on the scene carrying out investigations and officers do not yet know when the motorway will be reopened.
The Highways Agency are advising motorists to avoid the area and allow extra time for their journeys due to knock on delays.
Diversions have been put in place.
A Highways Agency spokesman said: “It is definitely going to run into rush hour, even the diversion routes are getting pretty full.”