BREAKING:Four people are confirmed to have died in a car and knife attack on Westminster in central London, including a police officer who was protecting Parliament and the suspected assailant, who was shot dead by armed police.
The attacker, dressed in black and armed with two large knives, drove a car over Westminster Bridge, ramming into members of the public before crashing his car into the rails outside the Houses of Parliament.
Police said the attacker, who is believed to have acted alone, then entered the gates of New Palace Yard and repeatedly stabbed a male police officer. He was shot by the officer's colleagues.
Two people were killed when the attacker's car mounted the bridge's pavement. Twenty others were injured in all, including two people who were standing by the railings where the attacker's black Hyundai came to a stop.
Metropolitan Police assistant commissioner Mark Rowley said the attack had been declared a terrorist incident, and Theresa May is due to chair a meeting of the Government's emergency Cobra committee later today.
Mr Rowley said a major counter-terror operation was underway, though police currently believe there is only one attacker. "Looking forward, people of London will see extra police officers on our streets, and we could call on the support of military," he said.
The attack began at around 2.40pm and proceedings in the House of Commons were immediately suspended. Deputy speaker David Lidington announced to the House that a police officer had been stabbed and the "alleged assailant shot by armed police".
Security sources have described the suspected assailant as a middle-aged Asian man, who attacked the officer on foot with a seven-to-eight inch knife.
Images have emerged of a man dressed in black, believed to be the suspect, being treated on a stretcher within Parliament grounds. A knife could be seen lying on the ground nearby.