Police said the policing of the target areas would be intelligence-led
The Mayor of London Boris Johnson has welcomed the Metropolitan Police's plans for officers to use more stop and search powers to prevent knife crime.
Under the plans announced on Tuesday police can search people without reasonable suspicion under section 60 of the Public Order Act.
The move came following a rise in fatal knife attacks in London.
But London Assembly Green Party member Jenny Jones said the stop and search powers may alienate young people.
The first team of 15 officers have already been deployed to an unnamed London borough.
Another five to 10 teams will take to London over the next week to 10 days and will target areas where intelligence suggests youths are more likely to carry weapons.
Mr Johnson said: "I welcome this new initiative by the Met and I believe that Londoners will also be reassured to see the police being proactive in the fight back against the terrible scourge of knife crime."
In his election manifesto Mr Johnson also pledged more weapons scanners for police at major transport hubs at large public events.
But Ms Jones, who sits on the Metropolitan Police Authority, said positive results would need to be seen very quickly in order for stop and search to be justified.
"Stop and search already disproportionately targets young people from ethnic minority communities and this aggressive approach has, in the past, had the long-term effect of alienating the young people it is seeking to protect, as well as having a damaging effect on community relations in London," she said.
She added that she will raise her concerns at the next MPA meeting on 29 May and will ask for a report into the potential long-term consequences of reducing the safeguards in the stop and search process.
The most recent knife victim in London was Steven Bigby, 22, who died from a stab wound to the chest after being attacked in Oxford Street on Monday.
Figures show 68 people aged under 25 have been killed in London since the beginning of 2007.
Of those, 13 were teenagers - nine of whom were stabbed.