City of London Police said they closed the popular landmark, which is a suspension bridge over the River Thames, while officers spoke to the person who had climbed on top of the railings. A spokesman said shortly after 11.30am: “Tower Bridge is currently closed while we deal with a person who has climbed the structure.”
Someone shared a picture from the scene on Twitter, which shows a person standing on the bridge in dark clothing.
A police officer can be seen speaking to the person.
The A100 was closed in both directions while the incident was ongoing.
Several bus routes were affected by the road closure, including the 42, 78 and 343.
Police reopened the bridge shortly after 1.30pm.
They said: “The bridge has now been reopened. Thank you for your patience.”
The person who scaled Tower Bridge is understood to have climbed down from the railings.
It comes as a protester was arrested after climbing scaffolding around Big Ben while dressed as Spiderman last week
Police were called to the scene shortly before 8am and it took them until 9.45am to convince the man to come down.
He was brandishing a poster that read: “No tier 3 lockdown for Great Northern Powerhouse unless an extra £2 billion for whole region from Chester, Stoke, Derby, Boston, Skegness to the Scottish Border.
“If not: Great Northern Rebellion.”
The man, aged in his 60s, was checked by paramedics before being arrested on suspicion of criminal trespass.
