A teacher has been stabbed with a knife at a Bradford school and a pupil is being hunted by detectives.
The male teacher, 50, was attacked at Dixons Kings Academy at 08:55 BST, police said.
He has been taken to hospital where his condition has been described as stable.
West Yorkshire Police are searching for a boy, 14, who ran from the school after the attack. He is described as Asian, with short dark hair and was wearing a blue uniform blazer.
Speaking at a press conference at the school's gates, executive principal Nick Weller said the "shocking" events were witnessed by a number of students and urged the boy to hand himself in.
He said: "I think the best thing for him to do is to report to the police station because he will be caught and the sooner that he does that, probably the better for him."
Mobile phone 'row'
A student who claimed to see the incident said it happened after the boy refused to hand his mobile phone to the teacher.
He said: "He just got something out of his pocket and stabbed him and ran off."
The boy said the teacher was polite and "never shouted" and described the boy as an "alright" person.
Police said a "considerable" search was under way.
Det Supt Simon Atkinson said: "We are conducting inquiries in the area to locate a suspect and I would like to reassure residents and staff that all necessary resources are being deployed to investigate this ongoing and clearly very serious incident."
He added there was no ongoing risk to pupils or staff at the school.
In a statement, the school said it was continuing to operate as normal and staff were working with police.
"All students are safe and calm and have responded with tremendous maturity during a very difficult time," it added.
The school said the knife was brought into school and security would be reviewed.
The NASUWT union said the circumstances surrounding the attack would need to be examined while Ian Murch, from the Bradford branch of the National Union of Teachers (NUT), described the situation as "difficult."
He said school stabbings were rare but it was the second incident of its kind in recent years, referring to the murder of teacher Ann Maguire by a pupil at a school in Leeds in April 2014.
Will Cornick, 16, was given a life sentence for killing the Spanish teacher at Corpus Christi Catholic College in Halton Moor.
Education Secretary Nicky Morgan said she was being constantly updated on the situation at Dixon Kings Academy.
Operating since September 2011, the academy, formerly called the King's Science Academy, was one of the first free schools to open and has about 700 pupils.
It has since become part of the Dixons academy group.
At its last Ofsted inspection in December, the school was told it required improvement. Behaviour of pupils was described as "improving" but a small minority were "disruptive".
The school recently hit the headlines after its founder and principal Sajid Hussain Raza was charged with fraud relating to his involvement with Kings.
He and two other members of staff - Shabana Hussain, 38, and Daud Khan, 43 - will stand trial in June 2016.
At the scene - Richard Edwards, BBC Radio Leeds
The school is at the centre of a two-part police inquiry.
One part is at the school site itself, where community officers are working to reassure parents, pupils and staff.
The second part is away from the school, as police search for the 14-year-old boy they want to speak to in connection with the stabbing.
Parents at the school gates say their thoughts are with the teacher, who's being treated in hospital.