No one is believed to have died in the crash on the new Sheppey crossing bridge in Kent.
It started around 7.15am local time and continued for 10 minutes as cars and lorries crashed into each other in visibility that was down to 20 metres.
There were reports of some motorists driving “like idiots” in the conditions before the crash that completely closed the A249 that goes over the bridge.
The scene was full of buckled cars, lorries and even a car transporter as people waited at the side of the road to receive help from the emergency services.
It was reported that people were trapped and a fleet of 30 ambulances and response vehicles went to the scene, with some casualties receiving treatment at the roadside.
Witness Martin Stammers, 45, from Minster, told Kent Online:
“It’s horrific. I’ve never seen anything like it in my life.
“All you could hear was cars crashing. We got out of our car and it was eerily quiet, with visibility down to just 20 yards.”
A Kent Fire and Rescue Service spokesman said: “There are no fatalities but ambulance crews are dealing with a large number of walking wounded casualties.
Firefighters have used hydraulic cutting equipment to release five people from their vehicles.
Kent Police said there were collisions at the top of the bridge and at the foot of the approach to it.
A lorry driver who saw the start of the accident used his truck to block the entrance to the bridge and stop more cars piling into the crash, a witness said.
A driver involved in the crash, Chris Buckingham, told Sky News:
“There was somebody, from what I’ve been told by the police there at the scene, who actually witnessed the first part of the accident, a lorry driver.
“He was going the other way and what he managed to do, which has probably saved lives, is he’s gone down to the end of the carriageway, gone across the roundabout and actually blocked off the road so no more cars could actually enter the dual carriageway before the emergency services got there.
“Whoever that guy is I’d like to shake his hand because he’s probably saved lives today.”