Police were called to Ancaster High School on Monday after staff saw what they thought might be someone with a weapon on the school's roof.

The staff member saw a young person on the roof with a "long object protruding from a backpack," Hamilton police say.

Officers went to the high school around 4:35 p.m. on Monday, securing the school as they investigated. But the youth wasn't there anymore.

They found a World Cup flag on the roof.

Police are considering the matter closed.