A lane on the M4 Prince of Wales Bridge has been shut while emergency repairs to a pothole are carried out.
The closure is causing slow traffic and tailbacks on the westbound carriageway, between junction 22 (M49) and junction 23 (M48).
The restriction came into place just before 10.30am, but it is not yet known which lane is affected or when it will reopen.
Traffic-watch website Inrix said: "Lane closed and slow traffic due to emergency repairs on M4 Prince of Wales Bridge Westbound between J22 M49 and J23 M48. A lane is closed for emergency pothole repairs, which lane is affected has not been specified."
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Highways England for the Severn Bridges warned drivers of the closure on Twitter and said: "#M4 #PrinceOfWalesBridge westbound J22 #M49 to J23 #Magor we currently have lane closures in place to deal with a pothole repair.
"Please approach with caution and obey signals set."
A tweet by "Live Traffic - M4" also alerted the public to congestion leading up to the bridge.
The full post on Twitter said: "#M4 westbound within J22 (#M49 / Avonmouth) - Congestion - Full details at https://MotorwayCameras.co.uk/Traffic#M4 (Updated every 5 minutes)"
Update: As of 12.30pm, the lane has reopened.
