A knifeman who stabbed a woman to death in a frenzied West London attack was knocked down by a car after a member of the public rushed to help the victim, witnesses have described.

       The Metropolitan Police said it had launched "an urgent investigation" after the incident, which took place in Chippenham Road, Maida Vale at around 9am on Monday.

       When officers arrived following reports of a stabbing, they also found a man had been struck by a vehicle. Both victims were pronounced dead at the scene.

       A local business owner has described the incident that took place on the street outside his shop, where he says one of his customers saw the attack and attempted to disarm the killer.

       Mo Ahmed, 27, was inside Am 2 PM Food and Wine on Monday morning when he heard commotion and a young woman screaming nearby. "There was a guy who ran up to a girl in the street and stabbed her – he had a knife and he was stabbing her again and again, all over her body," he said.

       "People were trying to intervene, there were people all around, shouting 'leave her alone, she’s bleeding'."

       "One of my customers lives nearby and was on his way to work when he noticed what was happening," Mr Ahmed said.

       "He ran to the attacker and managed to push him away from the girl. But then the attacker stood up and ran to attack my customer.

       "Then someone in a car – I don't know who – hit him, and the attacker fell down."

       After the attack, the customer came to Mr Ahmed’s shop to get water before returning home.

       "He was really devastated and shocked, he was shaking," Mr Ahmed recalled.

       Mulugeta Asseratte said he also witnessed the incident in West London.

       He said: "It is a very terrible incident and for it to happen on a Monday morning. I was coming up from the bakery to Chippenham Road and suddenly heard shouts of 'stop it, stop it' and it was a girl being attacked by a gentleman.

       "In any case, I'm a father of four daughters, such things do happen, and I tried to look and even say 'stop it' and it would not.

       "All of a sudden it moved to the street and no sooner than they reached the street than a car came and hit both of them. We were all shocked and shouting and my heart goes out to the families of this fatal incident.

       "This is something one sees in movies, not in real life."

       Jiyad Raad, who lives on Chippenham Road, witnessed the attack which took place right outside his front door.

       Mr Raad, who appeared visibly shocked, said: "I heard screaming outside my flat. I saw the guy get on top of her and stab her four or five times. In total he might have stabbed her as many as ten times. He was staring at her and he kept saying "take it, take it".

       "People kept trying to get him off her but he would chase them away and wave his knife at them.

       "We tried to stop him but we couldn't get to her because he was waving the knife.

       The woman had blonde hair and looked to be in her early twenties. He was completely focused on her and kept stabbing."

       Another resident, who did not wish to be named, said her husband had rushed outside after hearing their son scream that someone was being stabbed outside.

       She said: "I heard screaming and my son, who was looking out the window, came over and told me someone is being stabbed outside.

       "I saw the lady on the floor and the man on top of her and I thought he was beating her up but then i saw he had a knife.

       "My husband went out to help but no one could get close because he was waving the knife around.

       "The man with the knife was hit by a car. Everyone was trying to help the lady she was bleeding heavily. It was terrifying.

       "No one should have to see such an awful scene. There were lots of people walking past on their way to work.

       "The man who had been crushed by the car kept calling out 'help me, help me' but no one would go to him as we were all trying to help the woman."

       A police cordon has been placed on Chippenham Road, Elgin Avenue and Goldney Street in Maida Vale as police launch an investigation following the deaths.

       Detective Chief Inspector Neil Smithson said on Monday: “This morning an incredibly serious incident has unfolded in the Westminster area which has seen two people pronounced dead.

       “Our officers are on scene and are working to establish exactly what has happened. As soon as we have more information we will keep the public updated but for now we must avoid speculation and allow investigators to do their work.

       “What I can say at this time is that the incident is contained and we do not believe there to be any wider threat to the community.

       “We have spoken to a number of people already but anyone else who witnessed the incident, or who has information that could help us, is urged to make contact immediately.”

       Police are working to inform their families, and said that post-mortem examinations will be arranged.

       A spokeswoman for London Ambulance Service said: "We were called at 9.02am to reports of an incident on Chippenham Road, W9.

       "We sent a number of resources to the scene, including two ambulance crews, two clinical team leaders, an advanced paramedic, two tactical response units, a medic in a car, an incident response officer, and members of our hazardous area response team.

       "We also dispatched by road London's Air Ambulance.

       "Despite our medics' efforts, two people died at the scene."