The landmark’s Twitter account confirmed only pedestrians and cyclists could use it on Sunday morning.
City of London Police urged motorists to find alternative routes.
Tower Bridge remains open to pedestrians only at present.
— Tower Bridge (@TowerBridge) August 23, 2020
Traffic in central London was left gridlocked after the famous bridge failed to close after allowing a ship to pass along the River Thames on Saturday afternoon.
Queues of motorists and pedestrians were left waiting for at least an hour from both directions.
A witness said: “According to the security radios we overheard there are multiple failures.”
City of London Police said engineers rushed to fix the bridge as drivers were urged to avoid the area.
Its Twitter account said: “Tower Bridge is currently closed to pedestrians and traffic, due to a mechanical fault.”
One social media user said: “I’ve been stuck here for nearly an hour now… #TowerBridge.”
— City of London Police (@CityPolice) August 23, 2020
Another commented: “Yep, tower bridge definitely stuck! One side started to come down but the other didn’t! #towerbridge #londontraffic.”
The bridge connects the Square Mile financial district to Southwark.
In 2005, police closed the bridge for 10 hours after a technical problem meant the arms could not be lowered.
A spokesman for the bridge, which is owned and managed by the City of London Corporation, has been approached to comment.