At least three people are injured and several are in hospital in a mass stabbing incident near a school in Sweden.
The police are classifying the incident as attempted murder or manslaughter.
According to initial police reports, a fight broke out between two youth gangs who smoked together at a sports facility in Eskilstuna, which lies just over 62 miles west of Stockholm.
An unspecified number of 15 year olds have been rushed to hospital with knife injuries.
Three of the victims sustained wounds to the upper body, it has been said.
Police confirmed that no arrests have yet been made and that they are currently scouring the neighbourhood for four suspects thought to have carried out the attacks.
Drones and police dogs have been called in to assist.
It's believed the incident happened at the munktellarenan, an enormous 15,000 square km sports facility.
Arena manager Mattias Albers said the students had been at the munktellarenan for an "outdoor day", reported TV4.
Police spokesperson Dennis Strömberg Johansson said: "At the moment, several police patrols are in the vicinity of Munktellarenan, which is supposed to be the scene of the crime.
"Barriers have been set up.
"It must be an assault with at least one motive. The crime classification is attempted murder."
He told TV4 Nyheterna: "It is true that a serious crime is taking place, but in any case there is no shooting."
He added that "some kind of sharp object has been used."
An eyewitness told Swedish outlet Aftonbladet that he watched the fight from his window.
The man, identified only as Fredrik, said: "It was some kind of settlement, they fought each other. They were 20 against 20 who smoked together. I saw two people who had been stabbed."
Local outlet TV4 reported that the school headmaster is aware of the incident, but does not know any specifics.
Initially, it was reported that the stabbing happened at a school, but the principal clarified it did not and had happened at the sports arena.
Mr Albers, area manager for Arenas and outdoor activities in Eskilstuna, said the site is "temporarily calm" as police collect samples from the scene.
Employees have been ordered to evacuate the arena as the investigation is carried out.
