BBC reports there were a number of casualties, including a police officer.
London Ambulance said at least 10 people who were on the bridge were hospitalized.
Hospital officials confirmed the death of a woman and said others had “catastrophic” injuries.
According to police, three or four gunshots were heard.
Commons Leader David Lidington said the alleged suspect had been shot by armed officers.
London visitor Steve Voake told NBC News he was walking over the bridge when he heard screaming.
“I thought it was a road accident. There was lots of panic and confusion. Then I saw a shoe a ground. I one body on one side of the road and one body face down in the water with blood all around it.”
The incident comes on the first anniversary of the Belgian terror attacks in Brussels that killed 32 people.
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