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A tourist has captured the terrifying moment police opened fire outside Parliament as crowds fled a terror attack on Westminster Bridge.

People can be heard screaming as a huge crowd runs from the bridge seemingly moments after up to a dozen people were struck by a vehicle.

thumbnail for post ID 6526598 Terror in central London: Police officer stabbed and people mowed down by car outside Parliament

Seconds later up to four gun shots were fired as people continued to flee.

At least one person has died and a number of others have been hurt – including some with ‘catastrophic’ injuries.

A police officer was also stabbed and his apparent attacker shot by officers in a major security incident at the Houses of Parliament.

At least oen person was killed in the attack (Picture: Universal News And Sport)

There are also reports of people being seen in the river following the attack which happened on the anniversary of the Brussels attack.

MPs are in lockdown in the Houses of Parliament and a bomb squad is on the scene while armed officers secure the building floor by floor.

Scotland Yard says the attack is being treated ‘as a terrorist incident until we know otherwise’.

What happened outside Parliament?

Members of the emergency services work to help vicitms on Westminster Bridge, alongside the Houses of Parliament in central London on March 22, 2017, during an emergency incident (Picture: Getty)

A massive police investigation is under way after a terror attack in central London.

Here's everything we know so far about the Westminster attack:

Six people have died - a police officer, the attacker, a woman named as Aysha Frade, 43, US tourist Kurt Cochran, 75-year-old Leslie Rhodes and Romanian tourist Andreea Cristea who died 15 days after being pulled from the Thames.

The officer was Pc Keith Palmer, a 48-year-old husband and father with 15 years of police service.

A minute's silence was held at 9.33am to honour Palmer, whose police shoulder number was 933.

Ten people have been arrested and six addresses raided across London, Birmingham and elsewhere. One person has been released on police bail.

The woman was killed on Westminster Bridge as a number of pedestrians were mowed down by a grey Hyundai i40.

It is believed the man was also killed in the incident on the bridge.

Seven people are in a critical condition, and 29 have been treated in hospital.

The attacker, has been named as Khalid Masood by police, although he used several alias.

Armed with two large knives, he jumped out of the car after smashing it into the railings encircling the Palace of Westminster, fatally stabbing Pc Palmer as he entered the grounds.

He was shot dead moments later by another officer.

Theresa May told MPs he was a 'peripheral' figure, adding: 'He was not part of the current intelligence picture.'

To see all of our coverage of the London terror attack click here.

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