Delays on the Essex side are expected to continue until at least 9.30am.
A lorry has crashed on the M25 near the Dartford Crossing, causing police to close a slip road on the Essex side of the tunnel.
There is heavy congestion anti-clockwise, and the exit slip road for Lakeside shopping centre has been closed while emergency services recover the lorry.
Slow-moving and stationary traffic goes back as far as the M20 junction near Swanley.
Normal conditions at the crash site are expected to return 9.30am and 9.45am, with the most severe delays near Swanley and Dartford set to clear by 8am, according to Highways England.
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