A hero tour guide has described the moment he pinned down the suspected Islamist terrorist who carried out the London Bridge attack and stamped on his wrist until he dropped the knife.

Thomas Gray was one of the brave pedestrians on the bridge who risked his own life in the attack which has left at least two dead, not including the attacker, reports News.com.au.

Mr Gray said the attacker was wielding two knives, including one duct-taped to his hand, The Sun reports.

In one dramatic picture the terrorist can be seen lying on London Bridge after having been shot by police and chased by witnesses armed with the tusk of a narwhal — an ocean dwelling animal dubbed "unicorn of the sea" — and a fire extinguisher.

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"Me and my colleague Stevie were driving northbound over London Bridge and we sort of came up behind a double-decker bus and we noticed several people jumping over the central reservation (median strip) out to the right," Mr Gray told broadcaster ITV.

Bystanders held the man down until police could get to him. Photo / Twitter
Bystanders held the man down until police could get to him. Photo / Twitter

"We peered our heads around and saw there was one chap running away from five guys running him down with a fire extinguisher.

"So Stevie and I just thought what to do, and just ran towards it, left the cars where they were and tried to do our best to apprehend the suspect.

"When we got there he was wielding two knives, one was duct-taped to his hand so all I could do after the guys had held him down and were pinning him to the ground, tried to stamp as hard as I could on his wrist to try and release the knife as it were.

"Someone kicked the knife away, somewhere northbound up London Bridge and then after that the police armed response were really quick, got there almost instantaneously, and at that point we were told he had a bomb vest so we cleared house and got out the way.

Tour guide Thomas Gray stomped on the terrorist's hand until the knife duct-taped to his wrist was released. Photo / ITV
Tour guide Thomas Gray stomped on the terrorist's hand until the knife duct-taped to his wrist was released. Photo / ITV

"At that point, saw a guy get shot a couple of times and then I hit the deck. I hid behind a school bus full of little children … got the bus turned around and they went back south over London Bridge.

"At that point we were told to stay where we were, as we were then told he had a gun as well. So we just stayed put, heard another shot and a little explosion and we just heard 'run' so we just turned and hightailed it south over London Bridge and heard 15 or so gunshots."

Mr Gray's friend and fellow tour guide Stevie Hurst explained how he kicked the suspect in the head to try to disarm him.

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"Everyone was just on top of him trying to bundle him to the ground. We saw that the knife was still in his hand," Mr Hurst told the BBC.

"I just put a foot in to try and kick him in the head.

Bystander holds a knife after the incident on London Bridge. Photo / @HLOBlog
Bystander holds a knife after the incident on London Bridge. Photo / @HLOBlog

"We were trying to do as much as we could to try and dislodge the knife from his hand so he wouldn't harm anyone else."

One man dressed in a suit "ran through traffic" to seize the massive blade from the terrorist before walking away from the scene and ushering innocent pedestrians away.

Images from the scene show what appeared to be a second knife on the ground close to his body after the attack, which left two members of the public dead and at least 12 injured.

In videos circulated on social media, police can be seen throwing the hero bystanders off the attacker, screaming at them to stand back before a firearms officer aimed his weapon and shot the suspect.

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Two loud "pops" rang out on the bridge as a third hero who carried one of the attacker's knives from the scene walked away with his hands out to protect the other pedestrians on the bridge.