A seven-vehicle crash on the M25 near the Dartford crossing has led to warnings of heavy delays.
Traffic diversions were put in place after the incident near junction two on the anti-clockwise carriageway in Kent.
Kent Police said no serious injuries were reported but the the junction was closed for about two hours. It has since reopened.
The police helicopter was sent and a public address system was used to advise drivers caught in the tailbacks.
BBC travel news said all lanes had reopened by about 1400 BST after the accident at about 1120 BST, but traffic was still queuing.