The westbound stretch between junctions three and four, from Cosford and Tong to Shifnal, has been shut due to the incident since around 8.30am.
Three fire crews, and other emergency services, have been at the scene of the incident, with reports of "a substantial diesel spillage across all lanes".
Some drivers waited more than three hours to be released, when one lane was opened to let them through at around 12.45pm – while others face substantial delays as they follow a diversion route.
Speaking while waiting for the road to re-open one motorist said: "It has been more than three hours. Drivers are congregating along the western carriageway in small groups. There is little sign of movement at the scene. We can see the flashing lights of the emergency services but there has been no communication with the hundreds of motorists queuing. The hard shoulder has become very busy as both men and women have taken to relieving themselves."
Truck driver Peter Gavey on his way to Shrewsbury said: "I've pretty much written today off. I was due to drop off at 9am. This is the longest I've been stuck on the 54. Not sure why it is taking them this long."
A spokesman for National Highways said they were turning some trapped vehicles around – but the process is a lengthy one to carry out safely.
He said: "At 8.24am this morning an HGV travelling on the westbound M54 between junctions 3 and 4 caught fire resulting in a large spillage of diesel across lanes 1 and 2.
"The lorry has been completely destroyed in the incident which means recovery will take some time. We are treating the spillage in lane 2 with the intention of allowing trapped traffic past the scene in that lane, if it is safe to do so. We have also been releasing trapped traffic from behind by turning vehicles around since 10am but that is a slow process because of the care that has to be taken to ensure it is done safely.
"We also need to treat the spillage in lane 1, which is more severely affected than lane 2. It might be that the surface is too badly damaged and will need resurfacing either later today or overnight but we will know more once we see how successful our initial treatment is.
"We thank road users for their patience while we continue to deal with the incident."
The latest update from the organisation said: "The remaining traffic which is caught up within the #M54 westbound closure between J3 and J4 is now being slowly released in one lane past the scene."
An earlier updated listed a diversion route for drivers affected.
It said: "Westbound traffic is being diverted via the solid circle diversion symbol on road signs.
"Exit the M54 at J3 and take the third exit on to the A41.
"Continue on the A41 until the roundabout with the A5 and take the first exit.
"Continue on the A5 until the roundabout with the A4640 and take the first exit.
"Continue on the A4640 to re-join the M54 at J4."