Scotland Yard are on alert after the incident.
"Being treated as a firearms incident - police on scene," the Metropolitan Police said on Twitter.
There were conflicting reports with some witnesses saying they saw people being treated for injuries. Witnesses said they also saw a man with a knife.
MPs were placed in lockdown within the House of Commons chamber as the incident unfolded.
The House of Commons Leader told MPs that he believes a police officer was stabbed and the attacker was shot.