Calgary, and two other children’s hospitals were all hit with fake gun calls late Sunday night.
Calgary Police Service say someone called 911, saying that they and others were entering the Alberta Children’s Hospital with firearms.
Police searched the building, but nothing suspicious was found and the lock down was lifted an hour later.
Similar calls were made to the Stoller children’s hospital in Edmonton and Sickkids in Toronto.
Police are describing the incident as a case of “swatting” – when someone misleads emergency services into dispatching personnel for a false alarm.
Police believe that the calls are related and are continuing to investigate, although no arrests have been made.