One man has died and several others were injured in a crash involving a coach, a tanker and eight other vehicles on the M1 in Hertfordshire.
The tanker was carrying syrup which spilled onto the road
The accident happened in fog north of junction 4 just after 0400 BST.
Police said the man who died was a passenger in the coach and had suffered head injuries. Another person is in a serious condition with chest injuries.
Hertfordshire Fire Service said poor visibility due to foggy conditions could be a factor in the pile-up.
Fifteen of the 47 passengers on the coach, which was travelling from London to Luton airport, suffered minor injuries and were taken to a Watford hospital, a police spokeswoman said.
The victim was seated in the front seat of the coach. The other injured person was driving a car involved in the crash.
The motorway is closed northbound between junctions 1 and 5, between the A406 North Circular Road and Watford.
The entry slip roads are also shut northbound at junctions 2 and 4.
A Hertfordshire Fire Service spokeswoman said: "We had several calls reporting the crash, the first at 4.12am, and all the callers said the fog was a factor."
The coach was badly damaged
A BBC Three Counties reporter at the scene said two people in the coach had to be cut free.
All those injured were taken to hospital.
Fifty-two people in vehicles involved in the pile-up were unharmed, police said.
A Tate and Lyle tanker involved in the crash was carrying syrup which spilled on to the road.
A second tanker from the sugar firm was brought in to pump syrup from the first, while the remaining liquid was cleared from the carriageway.
The Highways Agency said the motorway may be reopened by late afternoon once the road surface had been inspected.