London terror attack: Social media lights up

Out of terror comes unity - following the attack in London in which five were killed and dozens injured, thousands have taken to social media to express their sorrow, grief and solidarity.

Unarmed police officer Keith Palmer was killed by a lone armed assailant on Wednesday afternoon (local time). He was shot dead by police.

Moments earlier, the attacker is alleged to have driven a Hyundai i40 at speed along the footpath of Westminster Bridge targeting pedestrians.

Around 40 were hurt with injuries ranging from moderate to "catastrophic".

Grainy footage of the car driving along the bridge also shows a woman falling into the Thames River below - she was rescued but had serious injuries.

The mid-afternoon attack sent the city into lockdown and sent people to social media to post photos and video of the scene - some of whom were criticised for filming before helping.

Others expressed their hurt, anger and prayers over the attack, with topics #PrayForLondon, Westminster and London Attacks trending worldwide.

Here are just some of them.