The crash, which occurred on the new Sheppey four-lane crossing bridge in Kent this morning, reportedly went on for 10 minutes as cars continuously collided with each other.
The scene on the bridge was a mass of tangled cars, lorries and even a car transporter as one witness said "all you could hear was cars crashing".
About 200 people have minor injuries, police said.
Six of those hurt in the collisions are thought to have serious injuries.
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The spokesperson said visibility was a problem over the bridge, but it was not clear whether that caused the pile-up.
Firefighters said they had freed five people from their vehicles on the southbound carriageway.
One witness said visibility was very poor but drivers were approaching the crossing with no lights.