A man has been arrested by armed police after an incident in Whitehall, near Parliament.
Scotland Yard said he was being held on suspicion of possessing an offensive weapon and planning acts of terrorism.
A witness described seeing two knives on the ground, one of which he described as a large bread knife.
A Metropolitan Police statement said there were no injuries in the incident close to the junction of Parliament Street and Westminster Bridge Road.
However, security remains tight outside Whitehall buildings following the terror attack last month. A helicopter is hovering over the scene.
On March 22, Khalid Masood killed four people when he drove along Westminster Bridge. He then got out of the car and stabbed PC Keith Palmer to death at the entrance to Parliament.
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