A large lorry fire in the westbound side of the Brynglas Tunnel at Newport has forced the closure of M4 causing widespread traffic disruptions.
As the fire raged, firefighters from South Wales Fire and Rescue Service tackled the blaze and brought the key commuter route under control.
Crews were called to the scene at 8.33am to control the fire and smoke.
The fire service said no other vehicles were involved in the fire and the lorry driver has escaped unhurt.
Adrian Moyes, incident commander for the fire service, said: "One lorry was well alight on arrival and crews were immediately employed to ensure no persons remained within this or any other vehicle within the tunnel."
Police have closed the motorway in both directions between J24 A48/A449 (Coldra) and J28 A48/A4072 (Tredegar Park) and the traffic has been diverted through the south of the city via the A48 Southern Distributor Road.
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