Eyewitnesses spoke of the moment they saw the human carnage left in the wake of Wednesday afternoon's attack on Westminster Bridge.

Read DW's live updates on the London attacks here.

A young man - who declined to give his name - had been on a bus approaching Westminster Bridge just after the attack. The driver asked all passengers to disembark at St. Thomas's Hospital.

Talking over the sound of sirens, he told DW: "I walked off the bus and saw someone laid down by the side with tourist guidebooks around them."

"As I walked along I saw more bodies on the ground, and people holding each other. I saw about 12 on the ground, laid out, and the next guy's leg is all broken and to the side," he said.

A woman from Manchester, who also asked to remain anonymous, was in London with friends when she saw the grisly incident unfold.

"I was on the bridge. I saw the car mow down a lot of people. I saw some people lying flat on the floor, and the police got there really quickly, and the ambulance did. One guy was dead."

Visibly shaken, she said: "I never wish to see anything like that again. Ever."

Terrorist incident 'not a surprise'

Police quickly cordoned off a wide area around the Houses of Parliament and closed Westminster Bridge and Westminster Underground Station. The civil service offices of Whitehall were placed on lockdown, and helicopters circled overhead while ambulances and police vans screeched past.

Curious tourists and schoolchildren approached the police cordon, eager to see what was happening.

The United Kingdom has been on a terror alert since the July 2005 attacks, in which a swift succession of three suicide bombings killed 52 people and injured hundreds on the London Underground.

For Sam and Osmond, both 17, this was one reason why the attack wasn't a surprise. But they did wonder why the attacker chose such a well-patrolled area of the capital.

"This is the safest place you could be, when there's loads of police around," said Osmond. If they were to do [an attack] on the train, I'd be really petrified. Here, it's a really stupid place to do it," Osmond said.

A mix of emotions

Around 5 p.m., workers began streaming out across St James's Park, trying to work out how to get home in spite of various station closures and discussing the disruption to their day.

Civil servants are not permitted to speak to the press, but one woman who worked at the Foreign Office and declined to give her name told DW that she hadn't initially known what was going on, and the sound of helicopters was not unusual in Westminster.

"I had a lot of work to do. Then I got all these messages from my children asking if I was okay. It was only when I saw a tweet that I realized something was going on. We had to stay in the building, but we were pretty chilled."

Caleb, a college student from Exeter on a daytrip to London, said that as a photographer, he came to see if he could get some good shots. His friend, Izzy, was more shaken. "It's a bit scary; you never know when it's going to happen."

Would Izzy visit the Houses of Parliament if they're open tomorrow? "No!" she said firmly. 

"It's just life. You can't not go places," Maureen, an American tourist, told DW. She was texting friends and family back home to reassure them of her safety, but she was emphatic that the incident would not impact her plans.

Only the policed cordons and the roar of the helicopters told of the day's horror as the sun set on the swans and daffodils of St James's Park.

For those who didn't witness the horror first-hand, years of being on high alert left them grateful to be safe. On Wednesday evening, their first concern was how to get home - and then, to watch the news to better understand the full extent of what just happened.

Read: Brussels marks one-year anniversary of terror attacks