A 15-year-old boy is in custody after allegedly firing a pellet from an air gun at another student inside a high school in Sydney’s east.

Police were called to reports a teenager had a firearm at Rose Bay Secondary College just after 1.45pm on Thursday.

Officers were told the boy fired a pellet into the back of another student using what has been described as a “BB gun”.

No one was injured.

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The teen was arrested and an air gun was seized as police begin inquiries into how the weapon was brought onto school grounds.