All motorway traffic was held after the crash at around 11.15am, whilst police, ambulance and fire crews attended the scene between junctions 39 (Shap) and 40 (Penrith).
The southbound carriageway was closed briefly due to smoke from the lorry fire but has since re-opened.
However, a full northbound closure remains in place from junction 39 at Shap to junction 40 at Penrith.
Accident investigation work is ongoing and police say the M6 northbound might remain closed 'for some time'. National Highways will then need to inspect the carriageway for any damage and carry out any repairs before the northbound carriageway can reopen.
It is not known whether anyone has been injured at this stage, but Cumbria Police and North West Ambulance Service have been approached for further details.
Northbound drivers stuck between junction 39 and the scene of the crash are being turned around and diverted off the motorway at J39.
There is also miles of congestion back to Tebay Services (junction 38) as drivers queue to exit the motorway at junction 39 to join the diversion route.
Staff at the North West Regional Operations Centre (NWROC) near Warrington and National Traffic Operations Centre (NTOC) at Birmingham have also set electronic signs across the motorway network to warn drivers of the northbound carriageway closure.
The diversions are currently adding around 50 minutes to northbound journeys, with delays on approach to the closure and along diversion routes, say National Highways.
A Highways spokesman said: "A diversion is in place from junction 39 using the parallel A6 but drivers wishing to avoid congestion along the A6 should seek an alternative route or delay their journeys."
Follow the hollow triangle diversion symbol.
- Exit J39, turn left onto B6261 westbound
- Turn right at junction of B6261/A6 and travel north on the A6
- Continue north on A6 through Shap, Hackthorpe, Clifton and Eamont Bridge
- At Kemplay Bank roundabout, take first exit onto A66 westbound
- At J40, take third exit onto M6 northbound.
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