Emergency personnel said they freed five people trapped inside their vehicles that were on a transit train crossing, the BBC said.
Witness said visibility was extremely poor but drivers still approached the crossing without using their vehicles' headlights, leading to a number of collisions.
Other witnesses told the BBC the scene was a sea of cars, buses and at least one tractor-trailer.
Driver Martin Stammers described the scene as "horrendous," saying he and his son saw cars under buses. He said visibility was only about 10-20 yards when he approached the crossing.
He said managed to squeeze through a gap at the scene.
"For 10 minutes afterwards, all we could hear was screeching, cars thudding into each other, [buses] crashing," he told the BBC.
Chief Inspector Andy Reeves said a number of people were injured but no one died.
While saying it was too early to give a definitive cause of the accident, Reeves said the weather will be considered a factor.
"I can confirm that it was, and it continues to be, very hazardous," he said of the foggy conditions. "It was described to me as a very thick fog and it was certainly low visibility at the time."
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