Eleven people were treated by paramedics at the scene, Kent Fire and Rescue told LBC. Other drivers were hurt too, but not seriously.
The M20 is shut both ways. It's expected to stay shut all night. Drivers are being sent round on the A20 instead.
That's everything we know.
Why this mattersSo let's talk about the scale of this.
Over 30 vehicles, on a motorway, in one night. That is one of the worst pile-ups Britain has seen in years.
But here's the thing. Not everyone agrees on the number.
Kent Police say more than 30 vehicles. National Highways posted online a few hours later and said up to 20. Two official bodies, two different counts, and neither has corrected the other.
So what caused it? Fog. Plain and simple.
Weather warnings had gone out for thick fog right across the UK that evening. It wasn't just Kent. Fog was reported near Sarre and Monkton too, and on the A299. Over in Buckinghamshire, freezing fog was also causing dangerous driving on the M4 at Taplow.
And here's a detail worth knowing. One driver told local reporters that smoke from fireworks at nearby Leeds Castle was mixing with the fog, cutting visibility even further on the way into Maidstone. Police have not confirmed that. It has not been tested.
So what happened on the ground? Kent Fire and Rescue say they were called a few minutes after the crash and sent three fire engines. Several people were handed into the care of paramedics from the South East Coast Ambulance Service. An air ambulance team turned up too, by car rather than by helicopter.
A few hours later, National Highways said recovery work was under way. But the motorway was still closed, and some drivers were still being turned back, nearly five hours after the crash happened.
Now, Kent has seen something like this before. More than a decade ago, over 100 vehicles crashed in fog on the Sheppey Crossing, also in Kent. That is still called Britain's biggest pile-up. Nobody died that day.
Nobody has died in this crash either, as far as anyone knows right now.
Kent Police want to hear from witnesses. Anyone with dashcam footage is being asked to come forward, quoting the reference number given by police.
What we don't know yet: how serious those two injuries really are, whether speed played a part alongside the fog, and when the M20 will reopen.
Right now, recovery teams are still out there working through the night. And the M20 is still closed.
