The incident began at around 12.30pm and has seen police flood the area, closing off certain sections.
According to reports, police were called following a suspicious letter addressed to an unnamed peer in the House of Lords.
A mystery ‘white powder’ was in the envelope, witnesses claim, causing much of Parliament to go into lockdown.
Members and peers are currently being kept away from the investigation - locked on a terrace.
Police confirmed they were investigating a suspicious package delivered to Parliament at around 12.30pm.
Nobody has been injured or taken ill following the discovery.
A spokesperson for the Metropolitan Police said: “A suspicious package has been delivered to the Houses of Parliament.
“Officers are at the scene examining the contents of the package.
“There have been no reports of any related injuries or illnesses at this time.”