Police said on Sunday they had arrested four young males and one girl in connection with the knife killing last week of a 16-year-old boy on a street in south London.

One of the arrests was made late on Saturday night and the other four early on Sunday morning. All five are being held at various south London police stations.

The four males are aged 16, 17, 18 and 22. The girl is 16.

Shakilus Townsend died in hospital on Friday morning after the attack in Thornton Heath the previous afternoon.

Police said they were looking for at least four people, including a young girl, who had been seen in the area armed with knives and a baseball bat.

They found Townsend with a stab wound in the entrance to a block of flats after receiving a call from a member of the public.

He was taken to St George's Hospital in Tooting, but was pronounced dead shortly after midnight.

His killing follows a spate of knife murders of teenagers in the capital this year.

Another 16-year-old, Ben Kinsella, was stabbed to death in Islington, north London, a week ago after a fight in a nightclub. Three teenagers appeared in court on Thursday charged with his murder.

His actress sister Brooke Kinsella, who appeared in "EastEnders", has appealed for young people to put an end to the violence that has plagued parts of the capital.

Metropolitan Police Commissioner Ian Blair said he would do everything in his power to tackle the problem.

London Mayor Boris Johnson said he was shocked by the murders and had warned his children not to intervene if they see a fight in the street.

On Wednesday, police said they had arrested 1,214 people in London during a six-week crackdown on knife crime.

A report from a committee chaired by Cherie Booth, the barrister wife of former prime minister Tony Blair, called on the government to set up a Violence Reduction Unit to tackle the national scourge of violent street crime.

The Street Weapons Commission report said the new unit should carry out an audit of gun and knife crime hotspots and look at the local prevention policies and what could be done to improve them.

"If we don't act now then the implications are serious for our future individual safety, community wellbeing and our society," it said.

"We believe tackling gun and knife crime should be an urgent national priority for everyone from the Government downwards.

"It needs coordinated and strategic leadership from the centre, effective enforcement to help reduce the attraction of knife and gang culture and effective intervention and youth services on the ground to divert those young people most at risk."