The M40 motorway is closed between junctions six at Watlington and junction five for the A40 at Stokenchurch.
The closure has been caused by a fire in a fuel tanker, which was driving along the southbound carriageway.
Traffic was stopped in both directions at around9pm and is currently being diverted off the motorway.
It is not yet known if anyone has been injured in the blaze or whether any other vehicles are involved.
Traffic reports also suggest there is trapped traffic in both directions caught within the closure.
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