The famous landmark was scheduled to open this afternoon to allow a large wooden tall ship to pass through, but it appears to have become jammed in place.
The two sides of the crossing became stuck at about 14:30 BST on Monday.
The city of London Police said the 127-year-old crossing had been closed to both traffic and pedestrians “due to technical failure”. Drivers too, have been warned to avoid the area while repairs are being carried out.
A spokesperson for the City of London Corporation, which manages the bridge, said investigations into the failure were ongoing but the source of the fault was currently unknown.
“We are working to resolve the issue as quickly as possible,” they added.
Social media was poured with numerous pictures and videos that show the bascules stuck in an upright position after being opened for the tall ship.
Bascules are the movable sections of road on the bridge that can be raised and lowered using counterweights. According to the Tower Bridge tourism website, the bridge opens about 800 times a year.
Spanning the River Thames, the 787-foot-long landmark was completed in 1894. Once powered by steam, since 1976 the hydraulic bascules have been driven by oil and electricity.
Upon its completion, the bridge was considered the largest and most sophisticated bascule bridge ever made
The bridge was also stuck in August 2020, with the official bridge Twitter account blaming “mechanical failure.”
Tower Bridge is a popular tourist attraction, and visitors can stroll along the walkways connecting the two towers.
The walkways were originally public, but they closed in 1910. They reopened in the 1980s as an exhibition space.