LONDON • The attacker was apparently a "thick-set man" wearing black clothes who made his way through the gates of London's Parliament grounds, just below the famed Big Ben.
He had something in his hand, resembling "a stick of some sort", said Mr Quentin Letts, British tabloid Daily Mail's parliamentary sketchwriter who witnessed the drama that unfolded yesterday afternoon in one of London's busiest areas.
"He was challenged by a couple of policemen in yellow jackets," Mr Letts told the BBC. Then, one of the policemen fell to the ground. "We could see the man in black moving his arm in a way that suggested he was stabbing or striking the yellow-jacketed policeman," he said.
The other officer ran for help and the assailant ran about 10m towards the entrance, before two plain-clothed policemen shouted a warning at him. When he ignored them, they fired at him two to three times and he fell.
Press Association political editor Andrew Woodcock saw what happened from his office window overlooking New Palace Yard, near the Houses of Parliament.
He told the BBC: "I heard shouts and screams from outside and looked out, and there was a group of maybe 40 or 50 people running round the corner from Bridge Street into Parliament Square. They appeared to be running away from something.
NEED TO BE ALERT
We need to be alert to prevent an attack; ready to respond to keep ourselves and others safe if we are caught up in one; remain resilient to carry on life normally; and stay united to counter those who advocate extremism and violence. Saddened by the loss of life and injuries.
DEPUTY PRIME MINISTER TEO CHEE HEAN, in a Facebook post early this morning on the attack in London.
"As the group arrived at the Carriage Gates, where policemen are posted at the security entrance, a man suddenly ran out of the crowd and into the yard. He seemed to be holding up a long kitchen knife.
"I heard what sounded like shots - I think about three of them - and then the next thing I knew, there were two people lying on the ground and others running to help them.
"Armed police were quickly on the scene and I heard them shouting to people to get out of the yard."
Eyewitnesses at the nearby Westminster Bridge said they saw a sport utility vehicle (SUV) mow down at least five people. Mr Radoslaw Sikorski, a senior fellow at Harvard's Centre for European Studies, posted a video on Twitter which showed at least two people lying on Westminster Bridge. "A car on Westminster Bridge has just mowed down at least five people," he wrote.
Mr Toby Helm, British newspaper The Observer's political editor, said in a tweet that he could see people stranded on the giant ferris wheel, London Eye, on the other side of Westminster Bridge, after it stopped running.
The attraction tweeted to say it was "holding all of our guests within our attractions as per tried-and-tested security procedures".
The Port of London Authority confirmed that a seriously injured woman was recovered alive from the Thames river.
Reading a short statement outside New Scotland Yard, Metropolitan police commander B. J. Harrington said a "full counter-terrorism investigation" is under way. "At this stage, I will confirm what we know has happened but I will not speculate. We received a number of different reports which included a person in the river, a car in collision with pedestrians and a man armed with a knife."