Metropolitan Police confirmed that at 7.37am London time today (4.37pm AEST) a car smashed into barriers outside the Houses of Parliament.
Armed officers could be seen surrounding the car before leading a man away in handcuffs, according to local reports.
Dozens of emergency vehicles have been seen swarming around Parliament Square with members of the public ordered to stay clear of the area, The Sun reports. Armed police remain at the scene.
A number of pedestrians have been injured.
London-based TV journalist Vincent McAviney tweeted vision of the scene, saying there was “lots of police activity”.
Breakfast TV in the UK carried footage of police officers pointing rifles into the silver car after it crashed. (Courtesy News.com.au)