Emergency services were called to Magdalen Bridge overnight, shutting the road to motor traffic.
Videos circulating on social media showed two fire engines on the historic Oxford bridge.
Oxford Bus Company and Stagecoach, which run bus services in the city, said their services were being diverted via Abingdon Road as a result of the road closure.
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The closure began at around 11.30pm on Friday night (June 9) and was lifted before 1am this morning.
Thames Valley Police said it had been called to the scene to support Oxfordshire Fire and Rescue Service and South Central Ambulance Service.