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London (CNN) -- At least seven people are confirmed dead and 51 injured in a "horrific" traffic accident in southwest England, Somerset police said Saturday.
The accident involved 34 vehicles, including cars, vans and large trucks, police said, some of which erupted into a "fireball."
Assistant Chief Constable Anthony Bangham told reporters more bodies are feared to be still trapped in badly burnt vehicles.
Some of the vehicles are "burnt to the ground" and unrecognizable, he said in a televised news conference after visiting the site. "This is a horrific scene."
The crash occurred about 8:25 p.m. Friday on the M5 highway near Taunton in Somerset, about 70 kilometers (45 miles) southwest of Bristol, according to the Devon and Somerset Fire Rescue.
Bangham said poor weather was likely to have been a factor, with wet roads after rain and banks of fog reported in the area.
Police were also looking into a nearby fireworks display to see if it may have played a role, he said.
He praised members of the public who showed "real bravery" in trying to rescue people from blazing vehicles, as well as the efforts of the emergency services.
"For a motorway incident, this is just about as big as it gets," he said. "This is a highly complex, very dramatic incident for our officers."
He said part of the highway would remain closed in both directions until at least Sunday.
About 15 fire trucks were sent to the scene, as rescue workers battled to extinguish blazing vehicles and cut free trapped passengers.
Avon and Somerset Police have appealed for anyone who witnessed the events to get in touch, especially if they have mobile phone footage.
CNN's Nicky Robertson contributed to this report.