Members of the public were praised as heroes on Friday after tackling a knife-wielding terrorist on London Bridge, unaware he was apparently wearing an explosive device.

Politicians, police officers, the Church of England's highest cleric and social media users lined up to praise the efforts of a group who pinned down and disarmed the suspect on the pavement before armed police arrived and shot him dead.

Several onlookers caught up in the dramatic events captured the incident on mobile phone footage.

"What's remarkable about the images we've seen is the breathtaking heroism of members of the public who literally ran towards danger, not knowing what confronted them," said London Mayor Sadiq Khan.

"Members of the public didn't realise at the time that was a hoax device and they really are the best of us -- another example of the bravery and heroism of ordinary Londoners running towards danger, risking their own personal safety to try and save others."

As three officers formed a semi-circle around the man, pointing their weapons, it took several seconds before the last man got off the suspect.

He was pulled away by one of the armed officers just a split-second before another officer fired.

A man in a suit and tie was seen standing by the suspect holding a knife in his right hand.

He then retreated several paces as armed police officers arrived. He urged people to get back after the two shots were fired, waving them away with his left hand.

Stevie Hurst said he saw people running away but felt "compelled" to jump out of his car and go towards the incident.

Prime Minister Boris Johnson paid tribute to the "extraordinary bravery of those members of the public who physically intervened to protect the lives of others"
Prime Minister Boris Johnson paid tribute to the "extraordinary bravery of those members of the public who physically intervened to protect the lives of others" AFP / DANIEL SORABJI

"The guys were just screaming, 'He's stabbed a couple of women'," the tour guide told BBC radio.

"Everyone was just on top of him trying to bundle him to the ground.

"I saw that the knife was still in his hand so I just put a foot in to try and kick him in the head: we were trying to do as much as we could to try and dislodge the knife.

"The guys that were there were just amazing. Absolutely incredible people. Heroes beyond belief."

Hurst said that as the suspect was being pinned down, he was "constantly screaming 'get off me'," but "we wanted to make sure that he's never going to do this again".

Prime Minister Boris Johnson paid tribute to the "extraordinary bravery of those members of the public who physically intervened to protect the lives of others".

"They represent the very best of our country and I thank them on behalf of all of our country," he added.

The Archbishop of Canterbury Justin Welby said: "What a privilege to live in a country where casual passers-by are so astonishingly brave.

"We can be united in celebrating such examples. Let those of faith thank God for the gift of such people, let all of us be glad," said the Anglican community's most senior cleric.

Main opposition Labour leader Jeremy Corbyn said: "We owe a deep debt of gratitude to our police and emergency services, and the brave members of the public who put themselves in harm's way to protect others."

Meanwhile John Nichol, the former British air force pilot held captive during the Gulf War in 1991, called the civilians "incredible, selfless heroes".