The school went into lockdown and as anxious parents gathered outside the campus they could hear the lockdown warning being repeated over the school's public address system.
There was no fight or threat involving the weapon, which police were seen removing in a paper evidence bag. It is believed to be a toy gun that fires harmless gel pellets.
Known as gel blasters, the toys are made to look like real firearms and their legality in Victoria is questionable because any imitation firearm that would appear to an ordinary person as real is deemed illegal and requires a permit for possession.
The News understands the weapon was sighted by another student, who reported it to teachers.
A student was taken from the school for questioning and several other students were spoken to as witnesses.
In a statement Victoria Police confirmed units were called to the school about 12.20 pm after reports a student had a handgun.
"Police attended and spoke to a 13-year-old and a 14-year-old boy. An imitation firearm was located and seized. Both have been interviewed in relation to possessing an imitation firearm and the investigation is ongoing," police said.
GSSC issued a message to parents that the school was out of lockdown and the students were safe. Parents fears were heightened when someone posted on Facebook about a gun at the school.
The lockdown was lifted around 1.30 pm.
