The M40 London-bound has been closed between junction 5 and junction 4 due to an ongoing coach fire.
The Highways Agency expect the road to remain closed until 8.30pm.
The incident, on the Buckinghamshire stretch of the motorway, happened shortly after 6.20pm.
Buckinghamshire Fire and Rescue Service said 20 firefighters were tackling the blaze but no-one is thought to be injured.
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