A technical fault left Tower Bridge stuck open on Monday afternoon, with cars and pedestrians stranded on either side of the London landmark.
A City of London Corporation spokesperson said: "Due to a technical issue, Tower Bridge is currently stuck in a raised position.
"We are working to resolve the issue as quickly as possible."
Pictures posted on social media showed the bascules stuck in the upright position after they were opened to allow a Jubilee Trust Tall ship to pass through.
The bridge opens around 800 times a year, which averages to around twice a day.
The fault has brought traffic in parts of central London to a standstill, with people wanting to cross over the bridge having to turn back or wait for the issue to be resolved.
Transport for London (TfL) has issued a traffic report for those travelling in the area, warning that "traffic is slow moving on both approaches to the closure".
The statement adds that East Smithfield has minor delays westbound, Tower Hill is slow eastbound with delays back towards Upper Thames Street Tunnel and there are also delays southbound on Mansell Street.
Additionally, Northbound Tower Bridge Road is queueing back towards Bricklayers Arms Roundabout, with TfL suggesting that people find an alternative route.