The sound of popping balloons at Carleton University prompted a campus-wide lockdown on Sunday after students called 911 because they believed shots were being fired.

The balloons were being popped on the third floor of the Tory building, according to Ottawa police.

The popping sounds led multiple people to call 911, starting at about 6:20 p.m. Some students took to social media to sound the alarm.

Responding officers and campus security personnel initiated a campus-wide lockdown while they investigated.

The lockdown was lifted after about 20 minutes when investigators determined there was no threat to public safety.