Last updated at 2:08 p.m. POLITICAL JOURNALISTS AND BYSTANDERS in London watched in horror as a police officer was stabbed outside the House of Commons on Wednesday afternoon, and the suspected assailant then ran towards the door used by members of Parliament to enter the chamber before being gunned down by plain clothes officers.

A "terrorist incident" at Westminster has left at least one person dead and others with "catastrophic injuries," according to doctors. pic.twitter.com/YYK4fEvllA — Channel 4 News (@Channel4News) March 22, 2017

Both the attacker and the officer later died of their wounds, along with at least two bystanders who were run down by the suspected assailant’s car on Westminster Bridge outside Parliament. Witness accounts of the attack were quickly shared on social networks.

Terror attack outside U.K. Parliament. 2 men down on road. Man with knife/machete got into Parliament and stabbed policeman. He's been shot pic.twitter.com/aYNktTiF4d — James West (@westicles69) March 22, 2017

Quentin Letts, a Daily Mail politics writer, told the BBC he saw a man in black using what appeared to be a knife to attack a police officer close to Big Ben, before being shot as he rushed towards the entrance to Parliament.

Just saw Parliamentary security men shoot a man who had attacked a policeman. Impressive reaction times by police. — Quentin Letts (@thequentinletts) March 22, 2017

Radoslaw Sikorski, Poland’s former foreign minister, shared video of bystanders rushing to help wounded people on the bridge in the immediate aftermath of the attack.

A car on Westminster Bridge has just mowed down at least 5 people. pic.twitter.com/tdCR9I0NgJ — Rados?aw Sikorski (@sikorskiradek) March 22, 2017

There are the cowardly attackers, and there are the people rushing to help the injured. They restore our faith, always, everywhere. — Karl Sharro (@KarlreMarks) March 22, 2017

David Lidington, the leader of the House of Commons, confirmed that the attacker was shot and killed on the grounds of Westminster Palace. Parliament was suspended and the members were forced into lockdown after the incident.

This is the moment the Commons was suspended in response to the stabbing of a police officer and a further incident on Westminster bridge. pic.twitter.com/ahETHz8Gzo — Channel 4 News (@Channel4News) March 22, 2017

Deputy speaker announces UK Houses of Parliament suspended after incident on Westminster Bridge https://t.co/WG8yXWpPVV pic.twitter.com/0SpfNcjAIv — BBC Breaking News (@BBCBreaking) March 22, 2017

Scene inside suspended House of Commons where MPs are locked in Chamber as part of major security operation at palace pic.twitter.com/iGqFEc0LZL — Steve McCabe (@steve_mccabe) March 22, 2017

Tobias Ellwood, a former soldier who is now a member of Parliament and Foreign Office minister, was among those who tried to save the life of the wounded officer.

Heroic MP Tobias Ellwood (here giving CPR to the injured police officer) lost his own brother Jon in the Bali bombings in 2002 pic.twitter.com/kA9hxN8OGL — Rupert Myers (@RupertMyers) March 22, 2017

Video of that scene was captured by Jaden Patel, a bystander, who shared the images online.

As the area around Parliament was sealed off, and first responders attempted to treat the wounded, political journalists shared fragmentary glimpses of the scene.

Paramedics desperately trying to revive injured in New Palace Yard pic.twitter.com/esmQtULO9q — Libby Wiener (@LibbyWienerITV) March 22, 2017

Shaky video of commotion after Parliament shooting. pic.twitter.com/ofGZwcMgaA — Patrick Daly (@thepatrickdaly) March 22, 2017

Looks like a Minister has blood on him

But he's ok. Think he was helping cops. — Paul Waugh (@paulwaugh) March 22, 2017

Helicopter landing on Parliament Square with emergency services. pic.twitter.com/g3LqOwp6bR — Jim Waterson (@jimwaterson) March 22, 2017

Brazilian tourist Renato Lincoln describes hearing three shots in quick succession. He took this picture of the car before police arrived. pic.twitter.com/8Ri1dDPBgd — Jim Waterson (@jimwaterson) March 22, 2017

The Metropolitan Police said that they were “treating this as a terrorist incident until we know otherwise,” and armed officers were on the scene.

Incident in #Westminster: We are treating this as a terrorist incident until we know otherwise — Metropolitan Police (@metpoliceuk) March 22, 2017

Officers – including firearms officers – remain on scene in #Westminster. More info as and when verified — Metropolitan Police (@metpoliceuk) March 22, 2017

The police also appealed to the public to show “restraint” in what images they share online.

Please use common sense and restraint in circulating pictures and videos of those that have been injured during the incident in #Westminster — Metropolitan Police (@metpoliceuk) March 22, 2017

Among those showing no restraint, and instead seeking to capitalize on the raw emotions following the attack, was the anti-Muslim extremist Tommy Robinson, a hero of Breitbart News, who rushed to the scene of the crime to rant about it being part of a 1400-year war between Islam and the West.

Far-right proselytiser Tommy Robinson is somehow down at Westminster with another far-right activist: pic.twitter.com/N83sOTh77e — Alex MacDonald (@AlexJayMac) March 22, 2017