The “much-loved” 15-year-old died this morning at around 8.30am on her way to school in Croydon.

Emergency services were called to Wellesley Road but the girl was pronounced dead at the scene.

Security worker Victor Asare said that blood ran “like water” and members of the public rushed to help after the girl was attacked.

A 17-year-old boy, who is believed to know the victim, has been arrested in connection with the incident.

Mr Asare said: “The blood was coming like water.

“A lot of people came, everyone came off the bus. (The suspect) ran away.

“Everybody was crying and screaming.

“The girl was on the floor.

“We tried to catch him and a lot of people tried to save the girl. I was so shocked, I was shaken.

“It’s somebody’s daughter.

“I finished work but couldn’t sleep, so came back, I wanted to see if the girl was OK.”

He said that the girl, who was wearing a green school blazer, looked as if she “didn’t want the boy to come closer” before he stabbed her with a knife that was “black, thin and about a foot long”.

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

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

A bus driver and a passer-by were seen desperately trying to save the girl before emergency services arrived, with police at the scene in Wellesley Road in Croydon within two minutes.

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.”

A large police cordon was in place as the police investigation into the stabbing continued, with forensics officers and a dog handler among those working at the scene.

A red double decker bus on route 60, three police vehicles and about a dozen officers, as well as a forensics tent, could be seen in the taped off area outside the Whitgift Centre.

Metropolitan Police Chief Superintendent Andy Brittain 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.

“This is an emotion I share and I know people across Croydon will be feeling the same.

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

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

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