The incident involved an empty waste tanker travelling southbound when the incident happened.
It collided with the central reservation barrier, crossed onto the northbound carriageway and came to rest in the verge next to the hard shoulder in the northbound carriageway, damaging the safety barrier in the verge between junction 41 and junction 42 of the motorway.
National Highways is working to re-open the southbound carriageway as soon as possible.
A Cumbria Police investigation into the incident is now underway.
National Highways is working to re-open the southbound carriageway as soon as possible with a lane three closure remaining in place for emergency barrier repairs.
However, the northbound carriageway is likely to remain closed into this evening’s peak travel period while the police investigation continues and arrangements are made to remove the tanker from the motorway and to carry out any barrier and carriageway repairs.
The incident happened several miles north of junction 41 with vehicles on the northbound carriageway stuck between the junction and the incident.
National Highways traffic officers are working to free drivers stuck behind the incident by turning them around on the carriageway back towards junction 41 where they will be able to join the diversion route or the southbound M6.
A diversion is now in place in both directions with drivers using the A6 to travel between junction 41 and junction 42.
Congestion on the diversion route is already very heavy so drivers should delay journeys or seek alternative routes if they are heading towards Carlisle or to Scotland.
National Highways' staff at the North West Regional Operations Centre (NWROC) near Warrington and National Traffic Operations Centre (NTOC) at Birmingham have set electronic signs across the motorway network to warn drivers of the carriageway closure.
Drivers are being advised to check traffic conditions before setting out on journeys. Live traffic information is always available at www.trafficengland.com or from National Highways’ 24-7 customer contact centre at 0300 123 5000. Updates will also be posted to @HighwaysNWest – National Highways’ regional Twitter feed.