UPDATE: Toowoomba police have issued a stern warning to young people that waving about replica guns is a silly and dangerous thing to do.

A 13-year-old boy seen with a realistic-looking replica handgun caused the lockdown of Toowoomba State High School's Wilsonton campus today

Police received a report of a young person armed with what appeared to be a handgun entering the school grounds about 8.30am.

The school was immediately locked down with police attending and cordoning off the area.

The replica gun was seized and the boy taken into custody.

Toowoomba Child Protection Investigation Unit officer-in-charge Detective Senior Sergeant Paul Hart said the act of carrying a handgun - replica or real - anywhere, let alone into a school, was very serious.

"This sort of situation is very concerning to police," he said.

"Not only did it send the school into lockdown and expend a lot of police resources, but if this young person had been seen by police brandishing this item, it could well have been treated as a real weapon.

The teenager will be dealt with under the provisions of the Youth Justice Act.

EARLIER: Toowoomba State High School's Wilsonton campus went into lockdown this morning after reports a student had brought a gun to the school.

A Queensland Police Media spokesman said it was quickly discovered that the gun was actually a toy.

"It was a kid who brought a toy gun into school and the school went into lockdown," he said.

"Police have spoken to him and the school has gone back to normal now."