A man has been detained by armed police outside the Palace of Westminster.
A bearded man, wearing black trousers and a grey sweatshirt, could be seen being held against the fence with his arms behind his back by a police officer.
The incident is not thought to be terror related.
The Carriage Gates entrance to Parliament is closed.
Scotland Yard said the man - aged in his 30s - was arrested on suspicion of possessing a knife.
There are no reported injuries.
A Parliamentary spokesman said: "We are aware of an incident outside the Palace of Westminster, which is being dealt with by the Metropolitan Police."
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules hereComments are closed on this article