BREAKING: Four people killed outside Parliament

Four people have been killed and 40 injured in an attack outside Parliament in what police are treating as a terror incident.

The assailant was shot dead soon after stabbing a police officer, who according to sources died at the scene after receiving mouth-to-mouth resuscitation.

A woman in her 40s and a man in his 50s were also killed after a car collided with pedestrians on Westminster Bridge before crashing into railings close to the entrance of Parliament. A number of other people are said to have been left with "catastrophic" injuries, with a seriously injured woman pulled from the River Thames.

On Wednesday afternoon The Commons were kept in lockdown amid reports of "further incidents in the vicinity" after gunfire was heard.

According to eyewitnesses, a man with a knife charged through the gates into the front yard of the Palace

Police say the incident is being treated as a "terrorist incident until we know otherwise".

Two people were seen lying within Old Palace Yard, immediately outside Westminster Hall.

Scotland Yard has said in a statement: "Police are asking people to avoid the following areas: Parliament Square; Whitehall; Westminster Bridge; Lambeth Bridge; Victoria Street up to the junction with Broadway and the Victoria Embankment up to Embankment tube.

"This is to allow the emergency services to deal with the ongoing incident.

"Officers - including firearms officers - remain on the scene and we are treating this as a terrorist incident until we know otherwise. "We thank the public for their assistance."

The Prime Minister is said to be unharmed, with eyewitness accounts of her being ushered away from the area.

The Mayor of London released a statement thanking the police and emergency services for their "tremendous bravery in exceptionally difficult circumstances".

If you have any information about the attack please call 0800 789 321