Four men, including a teenager, were stabbed to death in London on Thursday.
A 19-year-old was killed in an attack in Edmonton, north London, while two men in their 20s died a few miles away in Leyton and Walthamstow, east London.
A man aged 42 was found fatally wounded in Tottenham High Road, Tottenham, north London.
The day saw further fatal stabbings in West Bromwich, West Midlands and Crosby, Merseyside. On Friday a man was wounded in north-west London.
He was left critically ill with wounds to his back and stomach after a stabbing in Brenthurst Road, Willesden.
Prime Minister Gordon Brown said the stabbings were shocking and promised further measures to tackle knife crime would be announced on Monday.
Metropolitan Police Commissioner Sir Ian Blair said this recent spate of stabbings "graphically illustrates the need for everyone to pull together to put an end to this unacceptable violence".
In the first of Thursday's fatal stabbings, Javengis Jaronis was found at the back of a squat in Tottenham High Road, where he lived, at about 0400 BST.
He had suffered head injuries and slash wounds.
TIMELINE: KNIFE KILLINGS
0400 BST: Man found dying behind disused Tottenham pub
1430 BST: Teenager dies in fight in Edmonton
1730 BST: Stabbed man dies after crashing his car in Leyton
2020 BST: Man attacked in Walthamstow
At 1430 BST a 19-year-old youth was found by officers called to reports of a fight at a bedsit in Gloucester Road, Edmonton.
He was taken to hospital with multiple stab wounds and later died, becoming the 20th teenager to be killed in London this year.
Three hours later a 20-year-old man crashed his car in Downsell Road, Leyton, soon after being stabbed during a row with a group of men.
Later that night a man aged in his 20s was attacked in St David's Court near the junction of Wood Street and Forest Road in Walthamstow.
He was found with stab wounds to the head and chest and died about an hour later.
Sir Ian said: "I want to reassure the public that the MPS is doing everything possible both in terms of thoroughly investigating each case and in continuing to carry out proactive operations to get knives off the streets."
London Mayor Boris Johnson said: "I deeply regret that four Londoners have lost their lives in these tragic incidents. My thoughts are with the families of these men."
He added: "We need to do all we can to address the long term complex root causes of violence as well as ensuring the police are providing an effective deterrent to those who carry knives and guns.
"We are in this together and we all need to take responsibility.
"That's why we are talking to the government about bringing forward new measures next week that will help to address the underlying causes of knife violence."
According to the British Crime Survey (BCS), overall violent crime has decreased by 41% since a peak in 1995.
Knives are used in about 8% of violent incidents, according to the BCS, a level that has largely remained the same during the past decade.
But the BCS figures do not include under-16s, something which Home Secretary Jacqui Smith recently announced would change.