The students were rushed to hospital following the stabbing at a sports facility in the town of Eskilstuna, local media reported in Sweden.
The TV station had initially reported that the attack took place at a school but the headmaster later said the pupils had been at a different location at the time of the incident.
'We know very little at the moment,' the headteacher said. 'It is the school's students who are in another place.'
The students had reportedly been on a school trip to the local sports facility when a fight broke out between two gangs.
MNA/PR