More than 30 vehicles were involved in a collision which left two people seriously injured on the M20 in Kent late on Saturday, police say.
Officers were called to the scene at around 18:41 on the London-bound carriageway between junctions eight and nine, near Hollingbourne, Maidstone.
Eleven people were cared for by paramedics and two taken to hospital, Kent Fire and Rescue Service said.
An air ambulance crew, three fire engines and a “technical rescue unit” were sent to the scene, where National Highways said “thick fog” had been confirmed.
The road was shut in both directions early on Sunday and was likely to remain closed “for several hours while recovery and clear up operations continue”, the agency said.
Kent Police said one of the two people seriously injured had been taken to a hospital locally, and the other to a London hospital.
“Other drivers have sustained injuries not believed to be serious,” it said in a statement.
“Closures are likely to remain overnight while the incident is dealt with.”
The force has asked anyone with information about the incident or dashcam footage to come forward.