All traffic heading northbound was temporarily held from around 7pm as emergency services closed the motorway.
This follows what Cheshire Police is calling a ‘serious collision’ on Thelwall Viaduct, between junctions 21 for the A57 Manchester Road at Woolston and 20 for the M56 at Lymm.
Officers attended the scene and found a lorry had come off the carriageway and landed on the embankment below the bridge.
The driver of the lorry is not believed to have suffered any life-threatening injuries.
Trapped traffic is being released, with one lane open and three closed.
A diversion is in place with motorists following the hollow diamond symbol along the A50 Knutsford Lane into Knutsford and on the A57 Manchester Road.
A spokesman for Cheshire Police said: “Please be aware that a number of lanes are closed on the M6 northbound.
“The closures are expected to be in place for some time and motorists are advised to avoid the area and find alternative routes.”
A National Highways spokesman added: “Traffic caught within the closure of the M6 northbound in Cheshire, between junctions 20 for Lymm and 21 for Warrington, is now passing the scene of the incident via lane one.
“Thanks for your patience. We will have you moving as soon as we can.
“Three lanes of four remain closed due to significant barrier damage on Thelwall Viaduct.
“Traffic is passing via lane one only. Expect long delays on approach.”
These lane closures will remain in place for some time, and are expected to continue into the morning.
Cheshire Fire and Rescue Service confirmed that five fire engines from Warrington, Lymm, Middlewich, Chester and Powey Lane fire stations attended.
A rescue boat from Warrington Fire Station and an aerial appliance from Lymm Fire Station was also sent to the scene.
A CFRS spokesman said: “Firefighters were called to reports of a heavy goods vehicle that had left the carriageway of the M6 northbound between junctions 20 and 21, close to the Thelwall Viaduct.
“On arrival, they found that a HGV had left the carriageway and overturned on an embankment, falling approximately 60 metres.
“Crews used technical rescue equipment to lower themselves and reach the casualty, who was handed over to the care of attending paramedics.
“Crews have applied water to cool the HGV and are using bunding to contain a leak of approximately 1,000 litres of bio-diesel from the fuel tanks of the vehicle.
“Crews are now bringing operational activities to a close and are starting to leave the scene, handing over the incident to partner agencies.”
