Police quickly flooded the area, and cordoned off the streets surrounding the Houses of Parliament.
The House of Commons and House of Lords are both out of session from July 24 until September 4. ISIS claimed the 22-year-old British perpetrator of Libyan descent as one of its own.
Police also said a "number" of pedestrians were injured.
"At this early stage none of the injuries appear to be life-threatening". Officers remain at the scene.
Police have cordoned off the area around Westminster including several main roads.
The London Metropolitan Police noted that they are "keeping an open mind" as the investigation unfolds.
One man received treatment at the scene and two people were taken to hospital following the incident.
Metropolitan Police confirmed in a tweet that at 7.37am local time a auto collided with the barriers outside Parliament.
'Whether that area outside should be pedestrianised further, there should be further physical works done, I think is a matter that will be discussed no doubt between parliamentary authorities, us, the intelligence agencies and indeed the local authorities and the mayor'.
The auto crashed into a security barrier, one of many erected on key British sites in the wake of the September 11, 2001, attack in the U.S., and reinforced in recent years.
The area was the site of a terror attack in March 2017, when Khalid Masood ploughed a vehicle into crowds on Westminster Bridge, killing four people.
In March 2017, Khalid Masood, 52, killed four people on the nearby Westminster Bridge before he stabbed to death an unarmed cop in the grounds of parliament. A police officer gestures as he stands in a road in central London, after a auto crashed into security barriers outside the Ho.
"I was told basically to move away, to run".
"I was walking on the other side". I heard some noise and someone screamed.
Another witness, Ewelina Ochab, said the auto did not appear to have a front registration plate.
A man was dragged from the vehicle by police and arrested.