Teenagers were also stabbed in Blackheath, south-east London, Barking, east London and Tooting, south-west London on Tuesday, the Metropolitan Police said.
The Metropolitan Police said a boy, believed to be aged 17, received a slash wound to his face at about 6.05pm on High Road, Tottenham.
Blood splatters were being cleaned from the pavement outside a taxi office opposite Tottenham Police Station, around 160 metres down the road, on Tuesday evening.
An officer at the scene said a man had received facial injuries after "an altercation between two young groups", and that the two cordons were linked.
The boy was treated at the scene by the London Ambulance Service staff, who assessed the injury to be non life-threatening, and taken to an east London hospital.
Prime Minister Theresa May has pledged to hold a major summit in Downing Street on April 1 aimed at tackling the problem.
Metropolitan Police commissioner Cressida Dick said the last few years "undoubtedly have been the highest and most worrying levels in my service".
She added: "If you look at stabbings of young people I do think this is a new and tragic and worrying phenomenon."
A male, believed to be aged 18, was taken to hospital with injuries not thought to be life-threatening after the incident in Thyme Close, Blackheath, at around 3.24pm.
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