Hundreds more police officers will be on duty across London following four murders last week.
Metropolitan Police Commander Stuart Cundy said on Monday that it had been a “terrible” few days in the capital.
Mr Cundy said the force’s violent crime taskforce had carried out more than 21,000 weapons searches since April, seizing hundreds of guns and knives.
“That’s four families, four groups of friends and acquaintances, who have all been tragically affected by this senseless violence.”
Mr Cundy said the weeks around Halloween and bonfire night were always the busiest for police.
He said more officers were being deployed on the streets to help prevent further violent crime.
Mr Cundy appealed for anyone who knows that someone is armed to contact the police.
He added: “Many people will be concerned about this level of violence.
“We have hundreds of additional duty officers on the streets of every single borough.
“Only together can we bring down the level of violence in London.”
He said that the latest four killings, which have disproportionately affected young people, take the total number of murders for 2018 to 118.
Mr Cundy added: “We have had 118 murders in London, they do disproportionately affect young people, but not just teenagers.
“We are working closely with schools, we need to take more knives off the streets, because knife crime is undoubtedly one of the biggest challenges we are facing.”
Scotland Yard said 17-year-old Malcolm Mide-Madariola was fatally knifed on Friday outside Clapham South Tube station, south London, near where he studied.
The boy, from Peckham, south-east London, was attacked less than a day after 15-year-old Jay Hughes was killed in Bellingham, south-east London, by a stab wound to the heart.
Meanwhile, a man believed to be aged 22 was fatally stabbed in Samos Road, Anerley, south London, at about 12.30pm on Sunday.
And Rocky Djelal, 38, was fatally knifed at about lunchtime on Halloween as children played nearby in Southwark Park, Rotherhithe, south-east London.
Detective Chief Inspector John Massey, of the homicide and major crime command, said Malcolm Mide-Madariola was stabbed a “few minutes” after an “altercation” between two groups of boys.
“We are confident that our investigation will lead us to the person or people responsible, but we do need to speak with more witnesses and I am appealing for anyone with information to come forward,” he added.
Arrests have been made following a fatal stabbing in Samos Road #SE20 this afternoon. Police continue to appeal for information, pls call 101 quoting CAD 3251/04 Nov. To remain anonymous please call Crimestoppers on 0800 555 111. https://t.co/bInujsaQhY pic.twitter.com/95AmhE7ZLK
— Metropolitan Police (@metpoliceuk) November 4, 2018
Flowers were laid near the station for Mr Mide-Madariola, who died in hospital after being attacked at about 4.35pm.
Jay Hughes’ family, who described him as “very bright and brilliant at art”, was pounced on in a “premeditated attack” near a Morley’s chicken shop in Bellingham at about 5.20pm on Thursday.
The Metropolitan Police have yet to make any arrests in the killings of the two teenagers, but two men aged 19 and 21 were arrested on suspicion of murder over the older boy’s death.
The deaths came as debate continues over the effects of police budget cuts and what officers should focus their resources on.
London Mayor Sadiq Khan has previously blamed rising violence on £700 million cuts to the Met’s budget over seven years, with more expected to come.
On Friday, Mr Khan announced the latest measure in the “public health approach” to tackling violence, with a review of the most serious offences since 2014, to discover the trends behind attacks.
