Moorhead High: police are guarding the gates
The incident on the playing fields involved students of Moorehead High School in Accrington as well as people from the surrounding community.
The fight, which broke at lunchtime on Tuesday, stemmed from a personal dispute between two boys during the Christmas holidays.
A high profile police presence is continuing outside the gates of the school.
Arrests expected
Inspector Phil Cottam from Accrington Police said: "We want to ensure that pupils can come to and from school without any fear.
"The perpetrators of the violence will not be tolerated either in school or out of school.
"The police have an ongoing investigation."
Pupils and people from outside the school are being interviewed and the police say arrests are expected.
Intruder problems
It is understood friends of both of the two boys became involved in the fight after their row escalated.
The 16 excluded boys will remain away from school while the police investigation proceeds.
Joan Hazledon, acting head teacher at Moorehead High School said it had a history of intruders causing problems.
"I will not tolerate violence in school and if it means that I have to get the police in to help me... then I will do so," she added.
Schools in England are about to get new powers to crack down on persistent bullies and pupils who carry dangerous weapons.
New guidelines to be published next week will make it easier for head teachers to expel pupils.