A nurse who saw what happened said: “A man just went into a shop and took a knife and started stabbing people.

“The shopkeeper tried to get the knife away from him but he got away and stabbed a woman on a bicycle. The knife was really big.

“I saw three people who were injured - one of them might have been the attacker.

“I’m a nurse so I would have been willing to step in.”

A video shows one woman being taken into an ambulance. She was walking wounded, with a blanket around her.

London Ambulance Service said: "We have a number of resources attending an incident in Streatham High Road."

The Prime Minister has expressed his concern for those injured in the terror-related incident in south-east London.

Writing on Twitter, Boris Johnson said: "Thank you to all emergency services responding to the incident in Streatham, which the police have now declared as terrorism-related.

"My thoughts are with the injured and all those affected."

A 38-year-old man said: “I heard he was stabbing ladies, one on a bicycle, not the same one seen being taken into the ambulance. They were trying to save the victims.”

Another eyewitness said: “One woman was stabbed in the back and one man was stabbed in the stomach.

“The woman was saying ‘he stabbed me’. The man was in a bad way. People were screaming ‘stay with us’. It was a big wound.

“The police arrived and we heard ‘bang bang bang’. I saw the attacker lying down face down outside Iceland.”

The Mayor of London, Sadiq Khan, said: “A man has been shot dead by armed police in Streatham following an incident that is being treated as terrorism-related. A number of people are believed to have been stabbed.

“I am in close contact with the Met Commissioner and local representatives, and want to thank our police, security and emergency services staff for their swift and courageous response. They truly are the best of us.

“Terrorists seek to divide us and to destroy our way of life – here in London we will never let them succeed."