Drivers are being warned of severe delays due to two separate crashes.
One lane is closed on both the M1 and M25 causing long tailbacks.
On the M25, a lane is shut clockwise just after junction 24 for Potters Bar, with traffic extremely heavy back to before junction 22 for London Colney.
Highways England reports congestion stretches 10 miles with journeys taking around an hour longer.
Traffic queuing on the M25, with the left lane closed. Credit: Highways England
Traffic on the M25 is also slow between j20 for Kings Langley and j21 for the M1 due to a second collision.
One lane is closed northbound on the M1 after junction 8 for Hemel Hempstead, with queues solid back to before junction 5 for Watford.
Queues at Watford. Credit: Highways England
Motorists are advised to find alternative routes.
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