The witness Gerard Vowls, described seeing the attackers lunging at a woman and stabbing her, he told the AP. "I heard them say one thing: 'This is for Allah.'"
The incident, which killed seven and injured dozens more, began with a van charging into crowds of people, according to police. Minutes later in nearby Borough Market, knife-wielding men who had jumped out of the van and stabbed a number of people, the police said.
Vowls said of the three suspects, who were shot and killed by police after the attack, "I saw the look in their eyes, they were pure evil eyes, all three of them. ... They were like robots."
Vowls told the AP he threw a chair and a stool at the attackers to try to distract them.
"I went 'Oi, terrorists, cowards, Oi!" Vowls said.
He said one attacker "looked at me, he started running towards me and then he decided not to. Then I was screaming at them, picking up bottles from a beer barrel... I was just throwing it at them, trying to get them to chase me so I could get them out into the main road, draw them out to the main road to where the police could see them and obviously take them down."
"I could hear the police coming past but not stopping. ... I thought they were going up the wrong way, and that someone has to get the armed police," Vowls told the AP. "I shouted to the police officer woman, I said 'I know where they are.' She was 'where are they?'
Vowls recounted that he told the police he'd show them where the attack was happening.
"'They are stabbing people everywhere so get the armed police here, get the armed police,'" he said. "As we ran, me and the two officers, a man and a woman, we ran through the middle of the market again and I heard three bangs."
Vowls said of the woman he saw get stabbed, "I'd love to go and see her in hospital if she's still alive. Because I'm going to have her in mind for the rest of my life."
Witness Brad Myers was taking pictures of the Tower Bridge on Saturday night when he decided to take the stairs down to the river walk, he said Sunday morning. About two minutes later, he heard a loud noise and saw a van on the pedestrian sidewalk where he had just come from, he said.
"It was going through the pedestrian crowd that was there," Myers said of the van.
Myers walked back up the stairs and saw what appeared to be two victims and police rushing in, he said. He said the scene was a "real shock."
He added that it was a "chilling prospect" to think he could have been standing on the sidewalk if he had not gone down the stairs.
"I could have been right there," he said. "I really doubt I could have gotten out of there, to be honest."
Additional eyewitnesses described multiple stabbings at Borough Market to the BBC, with one man saying that he saw another man stab a victim twice with a long knife.
One eyewitness told the BBC that three attackers were armed with knives, and one of them had canisters strapped to his body.
The same witness described seeing a woman fall to the ground after being stabbed by one of the attackers.
Marc Poelmans of Belgium told ABC News he was having dinner at a restaurant just outside Borough Market when he saw outside the window a man walking down the street collapsed in front of a pub.
"It was clear he was bleeding heavily from the back. So I assume he was one of the stabbing victims," Poelmans said. "He was taken care of by a lot of bystanders. Somebody managed to flag down a police car and of course they started attending to the victim, as well."
"Maybe five minutes later the shooting started -- which was actually at the back of the restaurant because the back of the restaurant is a terrace overlooking the inside of the Borough Market," he said. "We crawled into the kitchen of the restaurant, we were on the floor for about 20 minutes. We heard continuous shooting."
He said armed police then came in and escorted them out, and they ran across the street.
ABC News' Janet Weinstein contributed to this report.