The accident happened on the northbound side near junction 16 of Nantwich, Cheshire and Talke, Staffordshire. Cows on that lane are past junction 15 of Stoke-on-Trent, an approximate 10-mile stretch.
Drivers can expect 90 minute delays on the northbound side.
The section is also congested southbound, with the tailbags reaching junction 17 for Sandbach and Crewe in Cheshire.
It is understood that the accident involved a car towing the livestock cart, but it is unclear if any animals were injured.
However, an air ambulance has landed, reports Stoke-on-Trent Live.
Alternative northbound routes include use of the A500 around Stoke-on-Trent from junction 15. Drivers can follow this around Newcastle-under-Lyme, Staffordshire, and join the motorway at junction 16.
Southbound motorists can leave the motorway at junction 17 and take the A534 through Sandbach and Crewe.
Then they should use the A500 at Weston, go past junction 16 and continue on the A500 past Newcastle-under-Lyme and Stoke-on-Trent.
They can then rejoin the M6 at junction 15 for Stoke.
Rescue services remain at the scene of the accident.
More to follow