A technical fault left Tower Bridge stuck open on Monday afternoon with cars and pedestrians left either side of the famous London landmark.
Pictures posed on social media showed the bascules jammed upright after being opened to allow a Jubilee Trust Tall Ship to pass through.
The fault brought traffic in part of central London grinding to a halt with people wanting to cross having to turn back or wait. Police are advising drivers to avoid the area.
Three double-decker buses without passengers that were parked on Tower Bridge were forced to back up as it remained closed.
Tourists and members of the public were told by bridge staff it could be up to three hours before the famous London landmark reopened.
Many of those waiting on the bridge were forced to seek shelter in nearby cafes and under the bridge itself as heavy rain showers set in.
A nurse on her way to work tweeted: "Tower Bridge is currently experiencing a technical fault and the bridge is stuck open. Slight pause to my walk #NursesActive but it was cool to see the bridge open for the first time in my life!"
Tourists passing the bridge seemed to enjoy the rare sight, describing its as a "good photo opportunity', while others saw a creative opportunity to think up a meme...
"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," the City of London Corporation said in a statement.
A traffic status update on Transport for London’s website said movement for motorists is slow on both sides leading up to the bridge.
It added: “East Smithfield has minor delays westbound. Tower Hill is also slow eastbound with delays back towards Upper Thames Street Tunnel. There are also delays southbound on Mansell Street. Northbound Tower Bridge Road is queueing back towards Bricklayers Arms Roundabout. Use other routes.”
Before lockdown Tower Bridge was one of the capital's busiest Thames crossings used by more than 40,000 people every day.
On average, Tower Bridge opens its bascules around 800 times a year, that's around twice a day. It was constructed between 1886 and 1894 and spent over a century as one of London's best-loved landmarks.
Tower Bridge was previously closed to the public last August after a mechanical fault meant it was stuck open for more than an hour.
Engineers fixed it and it reopened to motorists the next day.
In 2005, police closed the bridge for 10 hours after a technical problem meant the arms could not be lowered.