Police say a musical instrument may be to blame following a lockdown at the Calgary International Airport.

A video emerged on Twitter Thursday afternoon that showed people running through an airport hall as uniformed officers urged them to “stay back.” Moments later, the airport confirmed that a lockdown was in force and police were headed to the scene.

Const. Mark Smith with Calgary Police responded to the tweet, saying that security precautions were taken but “we can confirm there is no active shooter.”

Smith later tweeted, following a police investigation, “it was believed to be a musical instrument.”

The disruption is expected to affect some arrival and departure times as well as baggage delivery. The airport said in a tweet that it was working to return to regular operations “as quickly as possible.”