A bus driver and a passer-by desperately tried to save a teenage girl’s life after she was stabbed to death on her way to school in south London.

The pair were seen trying to resuscitate the injured 15-year-old on the pavement in Wellesley Road in Croydon after horror unfolded in the morning rush hour on Wednesday.

A mother-of-two, who wanted to be named only as Bridget, said: “I was on the bus before and came off and walked back down, I saw them resuscitating her.

“The driver was holding her, and a lady.

“The emergency services were already here when I walked back.”

She said two other schoolgirls, believed to be the victim’s friends, were trying to get back through the police cordon but were held back.

James Watkins, from Mainz World which runs prevention and intervention projects for children and young people, was with the girl’s family at the scene between 9am and 10am.

He said: “They were devastated and I would say more importantly in shock, I don’t think it feels real for them.”

The girl who died was a pupil at Old Palace of John Whitgift School, a private girls’ school in Croydon.

The school released a statement that said: “We are deeply shocked by the senseless and tragic death of our much-loved and valued friend and pupil.

“It will take some time for the Old Palace community to come to terms with this terrible news, and we will offer support to our pupils as we try to do so.

“Above all, we send our love and deepest sympathies to the girl’s family at this unimaginably distressing time.”

Footage posted on social media showed several police cars and ambulance vehicles near a bus in Croydon on Wednesday morning.

A boy who knows the victim has been arrested, the Metropolitan Police said.

Chief Superintendent Andy Brittain said: “Our immediate thoughts are with this young girl’s family who are facing the most tragic of news. Our officers are with the girl’s family to support them.

“I am in contact with the local community, who are clearly as concerned as we are about this tragic incident. I shall continue to update them throughout the day.”

Mayor of London Sadiq Khan said he was “absolutely heartbroken” at the news of the girl’s death.

Emergency services were called to Wellesley Road in Croydon at around 8.30am to reports that she had been stabbed.

Both the land and air ambulance attended but she was pronounced dead at the scene 50 minutes later.

Around an hour and 15 minutes after the stabbing police arrested a teenage boy in connection with the girl’s death.

Mr Brittain added: “My officers were immediately on scene to provide first aid and support paramedics.

“Acting on information provided to them, officers also worked closely with colleagues from across the Met and the British Transport Police to track a teenager in connection with the stabbing.

“I can confirm that an arrest was made at about 9.45am in the Croydon area. At this early stage we believe that he may have known her.

“A crime scene will be in place for some time, and I am grateful for the co-operation of residents.”

A spokesman for London Ambulance Service confirmed that three ambulance crews, an incident response officer, an advanced paramedic in a car as well as the air ambulance were sent to the scene.

A large police cordon was put in place outside the Whitgift Centre, with a red double decker bus on route 60, three police vehicles and about a dozen officers behind the police tape.

A bunch of flowers had been placed directly next to a forensic tent within the cordon.

The attack is not believed to have happened on the bus.

Forensics officers and a dog handler were working at the scene as the police investigation continued.

Transport for London said bus routes 60, 407 and 455 were being diverted away from the area “due to a police incident”.

Witnesses or anyone with information can contact police on 101 quoting reference CAD 1601/27Sep, to remain anonymous contact Crimestoppers on 0800 555111 or online.