A teenage cyclist was stabbed to death by a masked gang and two other men were also murdered in a weekend of knife carnage in London.

In Battersea a 17-year-old cyclist was ambushed and fatally stabbed as he tried to flee a gang in the early hours yesterday.

On Saturday, a man believed to be aged 43, was stabbed to death in Enfield by a group of men wearing ski-masks or hoods.

And last night a 60-year-old man was found dead from stab wounds at an address in Bow.

Residents in Battersea told how they raised the alarm after being woken at 1.25am yesterday by the boy’s screams of “help me, I’m dying”.

The teenage victim was reportedly found sprawled on the bonnet of a car in Ingrave Street on the York Road estate afer being chased by the gang.

Kemi Alli, 34, a care worker, told how the dying teenager screamed at her repeatedly “please help they have stabbed me” as she looked out her window overlooking the murder scene.

The mother of three gave emergency medical advice to a man who ran to the scene but was “devastated” that their efforts had not saved his life.

She said: “I heard screams and footsteps of people running away. I looked out the window and the boy was there looking at me and shouting ‘Please help they have stabbed me’.

“I called an ambulance and a man was next to him. I shouted at the man to apply pressure on the wound, because of my training I have some medical experience. I asked him if the boy was responding and he said ‘just’.

“It was obvious he was slipping away there was so much blood. I did all I could I was shouting at the man what to do then the ambulance arrived.

"I haven’t been able to sleep I just keep having flashbacks to the boy looking up at me and screaming for me to help him. I wish I could have done more.”

Witnesses described seeing a group of young men arriving on the estate in a car and then “hassling” passers-by earlier in the evening.

A 45-year-old neighbour said: “There were about six of them, they jumped out of the car and started chasing him immediately.

"He was on his bike but they caught up with him and stabbed him.”

Another resident said: “It was out of nowhere, there was some shouting and screaming and then the boy was laying there bleeding. Police surrounded the estate and told us all to go inside. The level of violence is increasing around here it is really frightening.”

Some witnesses said the gang were wielding machetes or large knives.

The 17-year-old, who has not been named, is the fourth teenager to be murdered in London this month alone, and the eighth this year.

The killings come as the Met revealed it is battling an surge in of knife and gun crime in the capital, with a 20 per cent increase in the number of stabbings.

Today Temporary Deputy Assistant Commissioner Duncan Ball said there was concern about the rise in knife crime and urged people with information about the weekend attacks to come forward.

He said : “We have seen an increase and the key to tackling this I believe is to stop young people from picking up knives in the first place.

“The police have to work together with the community and with schools and other groups to educate teenagers about the dangers of carrying knives.”

Police are appealing for witnesses to the attack in Exeter Road, Enfield where a 43-year-old was attacked and stabbed in the street.

Detectives say they are keeping an “open mind” about the motive for the assault which left the man lying in the street next to a plumber’s van.

Witnesses reported seeing his attackers fleeing through a wooded area as they reportedly shed bloodied clothes and tried to escape through Brimsdown Primary School’s playing fields.

Three men, aged 17, 18 and 21, were arrested and were being interviewed in custody today. The 18-year-old was also found with stab injuries near-by.

Paramedics fought to save the life of the man for over 45 minutes but he was pronounced dead at the scene at 2.15pm on Saturday.

Hannah Faulkner, 33, who witnessed the attack, said: “The gang were wearing masks so no one could recognise them.”

Her son added: “They were wearing ski masks so you could only see their eyes - they looked like ninjas.”

One witness said: “I heard a scream and I looked out of my window and I saw two guys in hoods running off.

“There was a woman crying kneeling by the guy, crying.”

Another witness, a 24-year-old student, described seeing a man being chased by three youths and stabbed by “a huge blade that looked like a sword. “

She said: “He put up his hands as if to say ‘don’t hurt me’ and they were all going for him. They stabbed him and then he stumbled back a few yards and collapsed.

“There were children there. It’s just horrific.”

Residents said a large bloodied kitchen knife with the blade broken off was found in a patch of grass just a few yards from where the man died.

Scotland Yard said they were called to reports of a man stabbed in the street asking for help in Bow Common Lanme at 11.20pm last night.

Officers attended and found the body of another man, aged 60, at a nearby address.

Another man, aged 54, was found with stab injuries.

The incident happened just yards from St Paul’s Way Trust secondary school.

Anyone with information should police on 101 or ring Crimestoppers anonymously on 0800 555 111.