The incident has closed the M4 through the tunnels in both directions The M4 motorway has been closed after a car caught fire in the Brynglas tunnels, Newport, say police.
A fault with the vehicle is thought to have started the fire in the tunnel westbound at 1107 GMT, said Gwent Police.
The eastbound tunnel reopened at around 12.45 GT but the westbound tunnel remained closed.
Traffic Wales said but traffic was being diverted onto the A48.
A structural survey is taking place.
The eastbound tunnel was closed for safety reasons and recovery.
Emergency services said six fire engines from Malpas, Maindee, Dyffryn and Cwmbran are at the scene.
Traffic cameras via the BBC Wales website showed queuing traffic building up westbound.
Traffic was reported to be queuing between J24 A48 / A449 (Coldra) and J28 A48 / A4072 (Tredegar Park).
Eastbound traffic from the Swansea direction is recommended to use the A465 J43 (Llandarcy) or the A470 J32 (Coryton).
Westbound traffic approaching Wales is advised to head North on the M5 to the M50.
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