Highways England have confirmed the M4 Prince of Wales Bridge will stay closed until at least 6am on Thursday.
At 10.30am, Gwent Police received a report that a lorry had driven down the embankment and onto land alongside the M4 Westbound at the end of the Prince of Wales Bridge.
Police are advising motorists to avoid the area due to heavy congestion.
The driver of the lorry, a man, was airlifted to hospital.
Anyone with any information or anyone who may have witnessed the incident or has dash cam footage is urged to contact Gwent Police on 101.
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