Four people, including a policeman, are confirmed dead following a terrorist attack at Parliament buildings and Westminster Bridge.
In the attack a vehicle mowed people down on the Westminster Bridge footpath.It is understood that the assailtant was also shot dead by police.
Frazer Clarke, 25, from Burton-on-Trent, was walking with his boxing teammates when he witnessed the horror.
He told the Press Association: "
We heard a loud bang and screaming and then I noticed some smoke. I thought it was a car crash.
"I looked towards the front gate and people were running, a police officer and a fellow coming to the gate with two knives.
"He was stabbing the police officer with the knives.
"He was wearing black tracksuit bottoms, a black of grey top and what looked like work boots.
"The police officer was stumbling and fell on the floor. Another police officer walked toward the guy with the knives and shot him twice. I didn't think they were proper bullets, they seemed like rubber bullets.
"Then people started shouting at us to get inside. Time stood still and I was shocked. The first thing I thought was this was a terrorist attack.
"It all happened so fast."
The terrorist attacked was shot by police and died from his injuries
It has also been confirmed that three French schoolchildren were among those injured when by the vehicle, the French government has confirmed.
The foreign ministry said they had been on a school trip to London.
A newspaper in France's Brittany region, Le Telegramme,
identified them as teenage pupils from a high school in Concarneau.One of them ended up on the car bonnet, according to witnesses it quoted.
Parents have begun gathering at the school.
The group, aged 15-16, were walking when they were hit by the car, the paper says.Pupils who were not hurt were put on a boat for security, after which they were able to return to the youth hostel where they had been staying since Sunday evening, it says.
The hostel is trying to get them back to France as soon as possible, the paper adds.
President Francois Hollande expressed his "solidarity" with the British people, saying "terrorism concerns us all and France knows how the British people are suffering today." The injured on Westminster bridge being attended to before the arrival of emergency services