A fight which led to the fatal stabbing of a 16-year-old boy at an Aberdeen school began after a row over biscuits, a court has heard.

Bailey Gwynne died of his injuries at Aberdeen Royal infirmary following the incident at Cults Academy last year.

Bailey suffered a stab wound to the heart during a fight with a 16-year-old boy, who cannot be named for legal reasons, according to a joint minute read out to the High Court in Aberdeen on Tuesday.

The court was told Bailey and the accused became involved in a fight shortly after Bailey refused to give a biscuit to another boy in the afternoon of October 28 last year.

A 16-year-old witness, who also can not be named, said: "They were punching each other, they were holding onto each other.

"[The accused] reached into his pocket and pulled out a knife or some sort of sharp object. I think it was his inside pocket."

He added: "[The accused] thrust it towards Bailey and it went into him."

Computing teacher Alasdair Sharp broke up the fight but told the court he was not immediately aware of the seriousness of Bailey's injuries.

He said: "I told the boys to follow me and walked them along the street [a communal area in the middle of the school] to take them to members of the senior management team.

"There was a small amount of blood on Bailey's shirt on the left side below the ribs."

He continued: "I turned around to see Bailey staggering towards the wall.

"I saw a trail of blood behind him. There was a lot of blood and he began to lose consciousness.

"One of the cleaners came over and applied pressure to his wound."

Earlier the trial heard from Cults Academy headteacher Anna Muirhead, who recalled the moment she first saw Bailey after the incident in Aberdeen on October 28.

Ms Muirhead, who was alerted by a member of staff at the end of the school lunch hour, said: "I was told: 'Anna, there's been a fight; it looks serious, we've called an ambulance'."

Ms Muirhead described how she went with the member of staff to the scene of the incident and saw the accused sitting nearby.

She said he appeared "distraught or upset" and explained how he had indicated that what had happened was "his fault".

"I saw Bailey lying on the ground with various members of staff next to him," she said.

"I knew immediately it was very serious. He was very pale [and] they had his shirt open."

Ms Muirhead said she could see blood.

A first responder arrived shortly afterwards followed by an ambulance crew, Ms Muirhead said.

She then went to speak to the accused, who she said told her: "Just take me to the police."

But Ms Muirhead told him the police were not yet at the school and brought the child to the deputy head.

She said she had discussed the dangers of bringing weapons into school with the boy several years previously.

The trial, which is expected to last five days, will continue on Wednesday morning.

In the days following his death, hundreds gathered to remember Bailey Gwynne, described as a "gentle, caring" boy.

Thousands of floral tributes were laid at the gates of Cults Academy and a candlelit vigil was held at Cults Parish Church.