Emergency crews scoured burnt-out vehicles Sunday following one of Britain's worst ever motorway pile-ups that triggered a huge fireball and killed at least seven people. More than a day after 34 vehicles crashed in foggy and wet conditions on the M5 motorway near Taunton in southwest England, rescue teams were still combing through charred metal littering the carriageway. Emergency services said 51 people had been injured in the accident that happened late Friday and warned the death toll was likely to rise. Investigators meanwhile stepped up efforts to determine the cause of the crash, indicating that as well as the wet and foggy conditions, a nearby fireworks display might have played a role in causing the pile-up. The huge crash sparked explosions and an inferno, reducing vehicles to cinders and leaving twisted, fire-blackened metal scattered across the carriageway. Footage taken at the scene showed motorists risking their own lives amid the flames to prise open vehicle doors and rescue people trapped inside. Witnesses described hellish scenes, with multiple explosions and towering flames sending a pall of acrid smoke into the night sky. "We could hear people screaming in their cars. It was utter carnage," said motorist Thomas Hamell, 25, who narrowly avoided the chaos as he came to an abrupt halt next to a jack-knifed lorry at the edge of the crash site. "We sat there and heard the thud of cars, one after another, hitting each other and thought we would be next." Assistant Chief Constable Anthony Bangham of the Avon and Somerset Constabulary told reporters: "Sadly I can now confirm that we believe we've had at least seven people died as a result of this incident. "I am also able to confirm that we've got 51 casualties. Many of those have gone to hospital." He said 34 vehicles were involved in the accident on Friday evening, "many of which are burnt -- and burnt literally to the ground." Detectives would be examining the possible factors involved, including the darkness, fog and groundwater, plus the fireworks display, he said. While casualties have been taken to two nearby hospitals and some treated at the scene, Bangham said others might still be trapped. Edmund King, president of the Automobile Association, said it was Britain's worst traffic accident in two decades, the last comparable incident being a 51-car crash on the M4 motorway in March 1991 in which 10 people died. Hospitals said the injuries ranged from simple limb fractures to more complex chest and abdominal trauma. Bev Davis, who saw the pile-up from her home close to the motorway, said: "All we could hear was the sound of a horn and then the flames got so high so quickly and the noise was horrific. "There must have been 200 metres (660 feet) worth of fire -- plumes of smoke were going up and everything was red." But tales of bravery also emerged amid the horror. Hamell said that he had managed to carry a baby to safety as chaos raged around him. The teacher described how he and his two travelling companions managed to get safely out of their car at the edge of the accident and help a mother and her young baby, whose car was severely damaged in the carnage.