Two people have died in a stabbing attack at London Bridge, in which police shot dead the suspect.
A further three were injured in the attack - declared a terrorist incident - and are being treated in hospital.
The suspect, who died at the scene, was wearing what is believed to have been a fake explosive device.
Videos on social media appear to show passers-by holding down a man. An officer arrives, seems to indicate to the group to move, and fires a shot.
A BBC journalist who was at the scene as it unfolded, said he had seen a struggle on the bridge, with several men restraining one man. Police then arrived quickly and a number of shots were fired at him, he said.
"My heart goes out... to everybody who has been affected by today's terrible and mindless events"— BBC Breaking News (@BBCBreaking) November 29, 2019
Met Police Commissioner Cressida Dick says "we must emerge stronger still from this tragedy", confirming 2 dead and 3 injured after London Bridge attack https://t.co/6ntnD2BqJu pic.twitter.com/A8G46RMY06
In footage shared on social media, the man could be seen being pinned down by members of the public. Another man in a suit could be seen running from him, having apparently retrieved a large knife.
Earlier, Neil Basu, the head of UK counter-terrorism policing, said in a press conference that male suspect was shot by specialist armed officers from City of London police and he can confirm that this suspect died at the scene.
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