He told BBC New he saw them stab a girl "10 times, maybe 15 times."
"She was going, 'Help me, help me' and I couldn't do nothing," he said
"I threw something - there was a bike on the floor. I threw something at them like a bike or a chair."
A man who gave only his first name, Ben, told BBC radio he "saw a man in red with a large blade, at a guess 10 inches (25cm) long, stabbing a man, about three times" near Borough Market.
Gerard Vowls, 47, told The Guardian newspaper he saw a woman being stabbed by three men at the south end of London Bridge.
He said he threw chairs, glasses and bottles at the attackers in a bid to stop them.
"They kept coming to try to stab me, they were stabbing everyone. Evil, evil people," he told the newspaper.
Alex Shellum, who was in The Mudlark pub, close to London Bridge, said he saw a bleeding woman in her early 20s stagger in.
"It appeared to myself and to my friends that her throat had been cut."
A taxi driver called Chris told radio station LBC he saw men armed with foot- long knives get out of the van that ploughed into people on London Bridge - the site of the first attack at 10.08pm on Saturday.
Holly Jones told the BBC a white van veered off the road and struck as many as six people. She said she saw at least four or five people on the ground.
Australian Labor senator Sam Dastyari, who was having dinner in the area, described the scene as one of panic, fear and chaos.
"It's graphic. There is no other way of describing it. It's confronting. The sheer sense and wave of panic that runs through people," he told Network Nine.
