Police officers should be "confident" to stop and search someone they suspect of carrying an offensive weapon, London's mayor has told the BBC.
Sadiq Khan backed the use of "targeted" stop-and-search in the capital, after six people were killed in shootings and stabbings in the past seven days.
An extra 300 officers are being deployed in areas of London.
Metropolitan Police Commissioner Cressida Dick denied her officers had lost control of the streets.
Mr Khan said stop-and-search was an "invaluable tool" for police when used properly - calling for "more targeted, intelligence-led" use of the power.
He said that local communities should play a role in protecting the public.
"You could be a mum or dad, big brother, big sister, a friend, girlfriend or boyfriend - who knows somebody carrying a knife," he said.
The mayor, who has faced criticism for not acting quickly enough to stop the killings, said budget cuts to policing and youth centres had harmed efforts to prevent the "evil" of violent crime.
But he added: "I'm not excusing criminality."
The Home Office said stop-and-search powers should be used in a "targeted way" and it was taking action to restrict weapons.
A spokesman said officers "will always have the government's full support" when properly using the powers, describing it as a "vital policing tool".
Chris Preddie, who mentors teenagers, and whose older brother Andrew was shot dead in Brixton in 2003, warned of a "ripple effect" of violence in the capital.
"It's become a culture now", he told BBC Radio 4's Today programme. "I'd be lying if I said I didn't want to go back for revenge [but] said to myself: would my brother want me to?"
Chief Constable Sara Thornton, the chairwoman of the National Police Chiefs' Council, said stop-and-search should not be used randomly but could work in crime hotspots.
Writing in the Daily Telegraph, she said officers were reluctant to use the powers because of what she described as the "chill effect" of political correctness.
She said policing "cannot address the social conditions that lead to violence" but while "stop and search or arrests are not a silver bullet, they are an important tool in helping to protect the public from violent crime".
But Ken Hinds, chairman of the Haringey Independent Stop and Search Monitoring Group, said stop-and-search too often focused on looking for drugs and he wanted more resources put into detecting knives and guns.
Prime Minister Theresa May curbed the use of the controversial tactic when she was home secretary amid concerns black people were being unfairly targeted.
The rising wave of violent crime meant the number of suspected murders in London in March was higher than that of New York.
Ms Dick admitted the Met was "stretched" but said her officers were doing "everything they can" to reduce street crime.
Earlier, she appealed for more public support for the police as it emerged the Met has opened 55 murder investigations this year, describing it as a "worrying time".