Police are "investigating an incident" in the Houses of Parliament.
A House of Commons spokesman said the investigation was ongoing but the building was not in lockdown, nor were any security alerts displayed on the annunciators around the Palace of Westminster.
No extra officers were visible at the main entrance at Carriage Gates.
A Commons spokesman said: "The police are currently investigating an incident on the Parliamentary Estate.
"While their investigation is ongoing, any questions should be directed to the Metropolitan Police press office."