A teenager who allegedly carried a loaded gun to school in his backpack was arrested Thursday, police said.

The 17-year-old Dorchester boy, who was not identified because of his age, was arrested at Jeremiah E. Burke High School in Dorchester after a school staff member found a handgun inside his backpack at 8:30 a.m., authorities said.

The 7.65 mm Deutshche Werk semiautomatic gun was loaded with a single round of ammunition, police said.

The teenager will appear in Dorchester Juvenile Court on charges of unlawful possession of a firearm, unlawful possession of ammunition and unlawful possession of a large-capacity feeding device.

No further information is available at this time.