Lara Jamil was walking towards a coffee shop before she heard a crash and saw a boy being run over.
The attacker then spoke to the woman and told her to “stay away” while brandishing two knives.
She told RT: “As I was crossing the road to go to the coffee shop, I heard a big crash, a big bang, and I looked behind me and a car just rampaged, drove over a boy. I thought it was a car accident.
“I ran immediately to the boy to see how he is – I could see blood, his head injury, he was shouting from the pure agony he was feeling at the time only to be faced by someone who’s just telling me ‘stay away, stay away’.
Lara Jamil said the attacker spoke to her before heading towards Parliament
I looked at him, I looked at his eyes and then his beard, and then he had two knives, telling me ‘stay away stay away’
“I looked at him, I looked at his eyes and then his beard, and then he had two knives, telling me ‘stay away stay away’. So at that time I thought ‘this is not an accident. This is an attack’.”
Describing the man, who was later identified as 52-year-old Khalid Masood, Ms Jamil said she could see “nothing in his eyes”.
She said: “One of the things I saw in his eyes – pure blankness. Nothing. He’s just killed a woman on the bridge – which I didn’t know at the time – he nearly killed a boy, he was going to go and kill more, and be killed.
“And still you can see nothing in his eyes. Blankness – you don’t see anger, sympathy, revenge, nothing.
London mourns terror attack at vigil Fri, March 24, 2017
The world grieves after an attacker killed three people and injured about 40 near parliament in London.
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Floral tributes are left after the vigil in Trafalgar Square, London to remember those who lost their lives in the Westminster terrorist attack
She said the attacker told her to "stay away" while brandishing two knives
“I do feel lucky… I thought I was really lucky. He could have just stabbed me.”
The witness said she then went to the other side of the road.
“I didn’t know where he went… I couldn’t see,” she said. “There was a shop just next to me, two guys talking, in a booth for souvenirs, selling souvenirs.
“And they were saying that it was an accident. I said to them, ‘No, it’s not. It’s an attack, he had knives in his hands. He is going to harm people’ – they totally dismissed me, they could not believe it.
“A few seconds [later] and we heard the bullets, the gunfire. So at that time I then ran to the boy to see how he is doing because I thought, ‘okay, the police have managed to shoot him’.”
A total of three people were killed on Westminster Bridge and police officer Keith Palmer was fatally stabbed before Masood was shot dead.
A police investigation into the London terror attack is ongoing.