Officers have arrived at London Bridge following reports of shots being fired, the Metropolitan Police have said.
Social media images show a number of police cars on London Bridge, with a lorry stationary across the middle of the bridge.
Police have cordoned off the bridge and the London Ambulance Service are on the scene.
Reports suggest a man was shot and killed by armed officers at London Bridge.
Police sources told Sky News a man was shot and killed on the bridge.
BBC reporter John McManus said he saw a group of men on London Bridge in what appeared to be a fight.
Armed police then quickly arrived and shots were fired . Eye witnesses told City A.M. that police were heard shouting “get down” before gunshots sounded.
Witnesses from the Fisheries Building, which overlooks London Bridge, heard police sirens on the bridge before the sounds of what they believed to be multiple gunshots.
“I heard at least 10 shots fired and a couple of bangs like flash bangs serious incident,” one witness, Dan Castleton, wrote.
Timothy Johnson tweeted: “Police shouting for everyone to move away. Real panic setting in at London Bridge.”
City of London Police have warned people to avoid the area at this current time.