Two men in their 20s have died and 11 others have been injured in a series of stabbings across London within 24 hours.
The Metropolitan Police were called to five separate incidents on Friday evening and enacted additional stop and search powers across Croydon overnight.
The incidents are not thought to be linked, Scotland Yard said.
There were also three other attacks on Saturday.
Police were alerted at 5.40pm to a stabbing in Willesden Lane, Kilburn.
Two males were found with stab injuries and one of them, in his 20s, was pronounced dead at the scene.
The second person, believed to be in his teens, was taken to hospital in a critical condition. There are no arrests as yet.
Earlier, police heard about a fight in Hadleigh Grove, Couldson, at 11.20am on Saturday, and arrived to find a man in his 20s had been stabbed.
He was taken to hospital with non-life threatening injuries, and two men have been arrested.
They were alerted to another stabbing, near the junction of London Road and Oakfield Road in Croydon, shortly after 3pm on Saturday.
A 24-year-old man has been taken to hospital following that incident.
On Friday evening, a 22-year-old man lost his life after being found injured at a property in Wisbeach Road, SE25. He was pronounced dead at the scene.
Two of the nine people wounded on Friday sustained serious injuries but neither is now in a life-threatening condition.
There have not been any arrests in connection with the murder inquiry that has been launched, police said.
But two people have been detained in connection with Friday's events. They are a man in his 40s, found with a stab wound at an address on Dingwall Road, Croydon, who was arrested on suspicion of affray.
A 38-year-old man has been arrested on suspicion of GBH.
The incidents on Friday night and Saturday were:
- At 6.56pm on Friday, police were called to reports of a man suffering a stab injury at a residential address in Chapman Road, Croydon. He was taken to hospital for treatment
- At 7.15pm on Friday, four men - all in their 20s - attended a south London hospital suffering stab injuries. Police say they received their injuries following an altercation in the Penwortham Road area of SW16
- At 8.10pm on Friday, officers attended a residential address in Wisbeach Road, SE25, and found a 22-year-old who had been stabbed. He was pronounced dead at the scene at 9.09pm
- At 8.51pm on Friday, police heard about two men, both aged in their 30s, attending a south London hospital with stab injuries. It is believed both men sustained their wounds during an incident in Jay Gardens, Chislehurst
- At 9.12pm on Friday, police were called to an address in Dingwall Road, Croydon, where they found a man in his 40s suffering a stab wound. He was subsequently arrested on suspicion of affray. A 38-year-old man was arrested on suspicion of GBH
- At 11.20am on Saturday, officers were called to reports of a fight in Hadleigh Grove, Couldson. They found a man in his 20s had been stabbed. Two men have been arrested in relation to that incident
- At 3.07pm on Saturday, police heard a 24-year-old man had been stabbed in London Road, Croydon. He was taken to hospital where his injuries were assessed as non-life threatening
- At 5.40pm on Saturday, police were called to Willesden Lane, NW6, where they found two males had been stabbed, one fatally. The other male was taken to hospital in a critical condition
Gold Commander for London this weekend, Ade Adelekan, said the incidents on Friday were being "treated as isolated".
But that did not make "this series of violent incidents any less shocking", he added.
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