A man, believed to be in his 20s, was reportedly stabbed St Anns Road, Harrow, on Sunday.
Police were called at the scene at 7.15pm, where the victim was pronounced dead, triggering a police hunt for the attacker.
A murder probe was launched after the man, who was found with stab injuries, died at the scene despite efforts by first responders.
Two other victims – thought to be teenagers – were reportedly taken to hospital with stab wounds following the attack.
The condition of the two injured victims is unknown at present.
A section 60 has been put into place for the whole of Harrow Borough until 10.49am Monday, 14 December 14.
The legitimate power entitles police officers to search people in a specific area and time period in order to prevent crime.
The Metropolitan Police have appealed for eye-witnesses or anyone with information that could help the inquiry to come forward.
The force released a statement with information into the crime on Sunday evening.
It read: “A murder investigation is underway following a stabbing in Harrow.
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“Crime scenes remain in place in and around the St Anns Road and Station Road area. Enquiries into the circumstances continue.”
Last month, London Mayor Sadiq Khan received criticism over his approach to knife crime in the capital following the violent killing of the hundredth teenager during his time as Mayor.
Shaun Bailey, Conservative London Mayoral candidate, blasted Mr Khan’s decision to significantly cut police funding.
He said: “One hundred teenagers have died since Sadiq Khan became Mayor. That’s one hundred mums who can no longer hug their children or see them grow up.
“This is a shocking trend. Knife crime rose by 38 percent in the year prior to lockdown. Homicides are at an 11-year high. And Sadiq Khan’s response is to defund police by £110 million.
“It is a terrible indictment of Sadiq Khan. Londoners deserve a safer, fairer and more affordable city.
“If Sadiq Khan won’t deliver it, then he should step aside for someone who can.”