A police constable has been stabbed while working behind the front counter of a north London police station, said Scotland Yard.
The policeman was injured at Wood Green Police Station, in Wood Green, at about 0315 GMT on Sunday.
He was taken to a north London hospital where he is in a stable condition.
A Metropolitan Police spokesman said a 15-year-old boy has been arrested in connection with the attack. He is being held at a north London police station.
Police said the attacker jumped over the front counter of the police station before stabbing the officer once in the abdomen. He then fled.
Officers are appealing for witnesses and information and are keen to speak to a man of about 6ft with "a shiny complexion" and a goatee beard who was spotted standing under a tree opposite the police station just before the attack.
He was wearing a blue top with a thin vertical stripe down its front.
They also want to trace a man, aged about 30, who came into the station to enquire about a family member five minutes before the stabbing.
They believe he might have seen the suspect entering or leaving the building.