A witness described seeing two knives on the ground, one of which he described as a large bread knife, BBC reported.
London Metropolitan police tweeted that the man had been arrested as the city's traffic authorities confirmed the Whitehall-Parliament Street was closed northbound due to a "police incident".
"Long delays" are expected, according to the authority.
A Metropolitan Police statement said there were no injuries in the incident close to the junction of Parliament Street and Westminster Bridge Road.
Security remains tight outside Whitehall buildings following the March 22 terror attack.
Attacker Khalid Masood killed a number of people when he ploughed his vehicle into crowds on Westminster Bridge.
British Prime Minister Theresa May's official residence at Downing Street is not far away from the Westminster Parliament building.
(This story has not been edited by Social News XYZ staff and is auto-generated from a syndicated feed.)
About VDC
Doraiah Chowdary Vundavally is a Software engineer at VTech . He is the news editor of SocialNews.XYZ and Freelance writer-contributes Telugu and English Columns on Films, Politics, and Gossips. He is the primary contributor for South Cinema Section of SocialNews.XYZ. His mission is to help to develop SocialNews.XYZ into a News website that has no bias or judgement towards any.