She was pronounced dead on the pavement despite desperate attempts by members of the public and emergency crews to save her.

A 17-year-old boy has been arrested after a 15-year-old girl was stabbed to death outside a bus on her way to an independent girls' school.

Old Palace of John Whitgift School, a private all-girls school in Croydon, confirmed that the victim had been a “much-loved and valued friend and pupil” and sent their condolences to her family.

Locals say they saw a group of schoolchildren getting off the No 60 bus outside the Whitgift Centre, where a row between the girl and boy - who were both in school uniform - 'spilled out' onto a street busy with pedestrians. 

Chevanice Thomas, whose friend claims to have witnessed the stabbing, said the girl had rejected flowers from the boy moments before he attacked her with a knife that resembled 'a sword'. Another witness claimed she heard the girl saying she 'didn't want to go out with him any more'. 

The bus driver and a passenger tried desperately to save the girl's life but she died at the scene at 9.21am. Officers arrested a 17-year-old boy in nearby New Addington at 9.45am. 

Today, Metropolitan Police Chief Superintendent Andy Brittain said detectives believe the boy knew the victim. He added that police are not looking for anyone else in connection with the incident. 

Old Palace of John Whitgift School is a selective independent day school for girls aged three to 11. It is consistently ranked as one of the best in London and is a sister school to Whitgift School for boys. 

Speaking to journalists at the scene, Mr Brittain said officers arrived within two minutes of being called and gave the suspect's age as 17. 

He said: 'This is every parent's worst nightmare, and I know the officers who responded this morning, along with our emergency service colleagues, are devastated at the victim's death.

The victim's family has been informed and our thoughts are with them at what must be an incredibly difficult time.

'We carried out urgent inquiries to find the suspect and within 75 minutes of the incident happening a 17-year-old boy was arrested in New Addington. He remains in custody and will be questioned by detectives.