BOSTON -- Boston police said they arrested five teenagers for trespassing at English High School Thursday morning about an hour after classes began, one of whom was charged with gun possession.

UNCUT: English High School Arrests

Original reports said there were four teenagers arrested, but the number increased by early afternoon.

Officers said they were called to the school on reports of a disturbance and found several teens involved in an altercation.

When they tried to break up the group, they said they noticed one teen focused on and reaching for a backpack. Inside, they said they found a loaded firearm.

Officers placed Walter West, 17, of Dorchester, under arrest and charged him with unlawful possession of a firearm, unlawful possession of ammunition, unlawful possession of a firearm on school property, resisting arrest and trespassing.

Several other teens involved in the disturbance fled the property, police said. They were eventually apprehended and charged with trespassing and disturbing a public assembly. They were identified as Damien Oliver, 17, of Dorchester; Tyrone Rutledge, 17, of Dorchester, and two juveniles, ages 16 and 13.

Police said none of the teenagers arrested was a student at the school. They were scheduled for arraignment on Friday.

There were no reports of injuries and the school was not placed under lockdown.

The English High School on McBride Street in Boston's Jamaica Plain neighborhood is the nation's oldest public high school, founded in 1821. It has more than 1,200 students.