4 youths have been arrested after Toronto Police found a loaded handgun in a student's backpack.

Police were tipped off by a CrimeStoppers call and went to Blessed Mother Theresa Secondary School in Scarborough around quarter to 2 on Wednesday.

The school was placed under a lockdown, but that was quickly lifted and all students were allowed to go home at a regular time.

All are students at the school.

The investigation continues into how the gun ended up in the school in the first place.