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A man was reportedly spotted on The Queen Elizabeth II bridge which was closed southbound last night.
The bridge was shut at about 7pm and traffic was diverted through the east tunnel while the closure was in place.
The road was reopened late last night.
People stuck in the traffic say a man was spotted, possibly threatening to jump, but this has not been confirmed.
Traffic officers were guarding the approach to the bridge and police were also on the scene.
Some motorists reported being stuck in delays of more than two hours.