A teenager has been stabbed to death at a busy railway station in south London.
Louis Johnson, 16, was found wounded at East Croydon station, just after 16:45 GMT on Monday, police said.
Emergency crews, including the air ambulance, were called but he died at the scene. Formal identification is yet to take place.
Det Insp Sam Blackburn, of British Transport Police, said the “senseless killing” happened “at an extremely busy time of the day”.
“For such a young man to lose his life in these circumstances is truly devastating,” he added.
“The incident was over within a matter of 40 seconds, but I know many other passengers or members of the public would have seen what happened.
“If you have not already spoken with police, please get in touch.”
The force said the teenager entered the station via a ticket barrier and met the suspect who immediately pulled out a knife and stabbed him.
Det Insp Blackburn said: “Alongside the Met, we’ll be increasing our patrols in the East Croydon area and we have authorised additional Section 60 stop and search powers.”
A Section 60 gives police officers the right to search people within a certain area if they think a person may be carrying a weapon or, in this case, a murder weapon.
At the scene
Greg McKenzie, BBC London
Monday night’s killing hasn’t necessarily come as a shock to local residents, but the scale of the violence involved seems to have had an impact.
One woman who lives close to the scene of the attack told me she saw a young man brandishing a machete, though this has not been confirmed, shortly before the attack.
“Croydon ain’t safe”, as one resident put it.
Knife crime has become a normal part of life, they say.
London Mayor Sadiq Khan said he was “deeply saddened” by what happened.
“Violent crime destroys lives and devastates communities,” he added.
Croydon Central MP Sarah Jones said she was “heartbroken”.
“Our first thoughts are with the family and friends who are facing what nobody ever should,” she said.
“I pay tribute to the work of the emergency services and station staff for their efforts.
“This brutal loss of a young life is another reminder that tackling violence must be our highest priority at every level of government and across our communities.
“I will not stop campaigning on this until our children are safe on our streets.”