Seven people have been killed and 51 injured in a 34-vehicle pile-up on the M5 in Somerset, and police fear the death toll may rise.
Officers said Friday night's crash, which happened close to junction 25 northbound at about 20:30 GMT, led to a "massive fireball" at the scene.
The cause of the crash is not clear but the road was wet and foggy in patches.
People concerned about relatives who may have been involved in the crash should call 0800 092 0410.
Earlier reports said more than 10 were feared dead and officers said some bodies may not yet have been recovered from the charred vehicles.
Of the injured, 25 were taken to Yeovil District Hospital; 17 of the more seriously injured are being treated at Musgrove Park Hospital in Taunton; and nine were treated at the scene.
Twenty-three of those taken to Yeovil have now been discharged.
The motorway is closed between junction 24 for Bridgwater and junction 25 for Taunton and will remain shut until at least Sunday morning.
After the crash, motorists suffered five-and-a-half hour delays on the M5, as traffic backed up for miles.
Assistant Chief Constable Anthony Bangham, of Avon and Somerset Police, appealed for witnesses to contact the police to aid what he said would be a "very thorough investigation" into the crash.
He said the crash scene was "horrific" and there would now be a multi-agency "forensic examination" of the area, where many vehicles were burned to the ground.
"The incident was very, very challenging and on arrival crews were faced with literally one massive fireball," he added.
"Most vehicles were well alight and most continued to burn for a considerable time."
Police could not confirm the age or sex of the dead, but Mr Bangham told reporters four of the casualties were in one vehicle.
Motorists who used the road before the crash said there was standing water on parts of the carriageway, following a day of heavy rain in the county.
Police said they would be investigating whether appropriate safety measures were in place regarding a fireworks display which was taking place at Taunton Rugby Club near the motorway.
The club have made no comment on reports that bonfire smoke may have drifted onto the carriageway, but confirmed the display took place between 20:00 and 20:15 GMT.
Tom Hamill, of Wells, who witnessed the accident, said: "I'd slowed right down and had veered into the central reservation and I think that saved our lives - the fog lifted and I saw utter carnage.
"The thing that made me realise how bad it was, was you could hear the thud of cars hitting into lorries: One car overtook us going at about 60 or 70 miles an hour and just crashed straight into a lorry.
"I could hear people screaming and shouting. One woman who was carrying a baby and child was desperate - I helped the child over the central reservation and we all just tried to get as far away from the fire as possible."
Motorist James Spurling, of High Wycombe, said: "I had just passed the spot where the accident happened just before 8:30.
"I, along with a car on the inside lane, had to brake very sharply as we both hit a solid wall of white that came out of nowhere.
"The visibility was instantly down to less than three metres and I would say was approximately 200 yards thick, once out the other side it was completely clear."
Transport Secretary Justine Greening said it was too early to consider what measures could be taken to prevent similar accidents.
Paying tribute to "real acts of heroism" by emergency crews, she said: "Our hearts are with the people who have been affected by this."
Traffic is being diverted via the A38 but heavy queues are reported on the route and police are advising people to avoid the area entirely if possible.
North Petherton Carnival, which was due to be held just to the north of the crash site on Saturday night, has been cancelled as a mark of respect.