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Two lanes had to been closed earlier and traffic queues soon build up after a vehicle broke down at the Dartford Tunnel.
The problems were between J1a of the M25 for the A282 and Swanscombe and J31 for West Thurrock.
The right-hand tunnel was closed but has now been reopened.
Meanwhle, on lane is closed after an accident involving two cars on the M25 anticlockwise between J3 for the M20/A20 (Swanley Interchange) and J2 for the A2 (Darenth Interchange).
Lane one (of four) is closed in the queues heading to the Dartford Tunnel.
There is still stationary traffic due to the earlier break-down, but all lanes have now been reopened, but drivers are being warned their journeys could take an extra 40 minutes.
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