People are using #PrayForLondon on Twitter to show solidarity with the UK after the terror attack in Westminster
The incident occurred on Westminster Bridge and in the grounds of the Palace of Westminster.
People have been using social media to #PrayForLondon and show solidarity with the UK capital after a terror attack took place in Westminster.
Musicians, actors and sports stars from the US and elsewhere were among the many to tweet the hashtag.
People have been sharing their thoughts and messages of hope alongside it.
A number of pedestrians were mowed down by a car on Westminster Bridge, before the attacker jumped out of the car and fatally stabbed a police officer in the grounds of the Palace of Westminster.
Four people have died, including the police officer and his attacker who was shot by another officer.
More than 20 people are reported to have been injured, while one woman was rescued from the Thames and treated for serious injuries after being pulled from the water.