While initial reports suggested fog and wet road surfaces were partly to blame for the huge collision, police said they have now zeroed in on the fireworks show after evidence taken from witnesses indicated that black smoke emerging from it may be the main culprit.

Rescue workers have described the road accident as one of the deadliest in the country in years.

``We believe from the witnesses and from what we're being told that it was smoke and not fog,'' Assistant Chief Constable Anthony Bangham told reporters. ``The vehicles and people who were entering into the smoke bank have just described it as being impossible to drive through and that, of course, causing them to brake.''

Friday night's crash on the M5 highway in southwestern England saw dozens of cars and industrial trucks consumed by flames, with intense fireballs that made it difficult for rescue workers to get near the vehicles.

The fireworks display in a nearby rugby club was one of many organized over the weekend across Britain to mark Guy Fawkes Day, an annual commemoration of the English activist who tried to blow up Parliament in the 17th century.

The probe into what caused the accident will be taken up by crime teams and road police, Bangham said.

Police have finished removing all vehicles from the highway in Somerset, and the roads have partly reopened. (AP)