Five people were killed, including the assailant, and 40 injured after being run over and stabbed in a terror attack at the heart of Britain's seat of power attributed by police to "Islamist-related terrorism".

UK Parliament attack: leaves 5 dead and 40 injured

The lightning attack unfolded across Westminster Bridge in the shadow of Big Ben, a towering landmark that draws tourists by the millions and stands over Britain's Houses of Parliament -- the very image of London. 

Emergency services at the scene outside the Palace of Westminster, London

The attacker was shot dead by police within the perimeter of UK Parliament

Conservative Member of Parliament Tobias Ellwood, centre, helps emergency services attend to an injured person outside the Houses of Parliament, London

The attacker used a car to run down several pedestrians on the iconic Westminster Bridge.

Emergency services staff provide medical attention close to the Houses of Parliament in London

At least one woman and one other person were killed by the vehicle and others were left with "catastrophic injuries,"

In this image taken from video  police officers gather around a car adjacent to  Houses of Parliament in London

The driver then rammed his car into the Parliament fence and fatally stabbed a police officer as he tried to enter the building. 

Man injured man sits covered with a blanket as emergency services staff provide medical attention to injured people on the south side of Westminster Bridge

British port officials said they pulled a woman from the Thames River after the attack. She was injured but alive.

An Air Ambulance comes in to land as emergency services attend to injured persons outside the Houses of Parliament, London

In a statement from Downing Street, British Prime Minister Theresa May called the incident a "sick and depraved terrorist attack."

Emergency services on Westminister Bridge after a policeman was stabbed and his apparent attacker shot by officers

"The location of this attack was no accident," PM said in a statement outside her 10 Downing Street office.