The motorway has been closed since 2.30am between junctions 32 (Preston, M55) and 33 (Lancaster South, A6) after a lorry overturned, spilling oil and fuel across the carriageway.
As of 3.30pm – 12 hours after the crash - efforts are ongoing to recover the HGV and carry out repairs to the carriageway.
National Highways has not said exactly when the M6 is likely to reopen, but it estimates that it is likely to remain shut past rush hour and into the early evening.
Motorists affected by the closure are now being advised to plan ahead and allow additional time for rush hour journeys this evening.
A spokesman for Lancashire Police said: “We’re still at the scene and the recovery is ongoing. Hopefully we can update you later this afternoon.”
The force added that the lorry driver was not injured in the crash.
There are still reported delays of 90 minutes above normal travel time and around eight miles of congestion on the approach to junction 33 in Lancaster, where traffic is rejoining the M6.
But others have reported being stuck in long queues for over two hours on the A6, where northbound traffic is being diverted through Barton and Garstang towards the motorway at Lancaster.
Traffic is currently queued back to junction 28, with traffic now exiting the motorway at Leyland and heading into Preston via Lostock Hall or Bamber Bridge.