BOSTON (WHDH) - BOSTON (WHDH) – The sound of people popping balloons in a building at Simmons University was mistaken for gunshots Thursday afternoon, prompting a massive emergency response and several shelter-in-place orders, Boston police said.

Officers responding to a report of what sounded like gunfire in the college’s science building shortly before 3 p.m. advised the university, along with many other area schools, to go into lockdown mode.

As officers descended on the campus, Simmons University sent out a text alert warning students of a possible active shooter and ordering them to stay in their dorms, stay away from windows and run if possible.

“I was in my psychiatric nursing class and all of sudden we saw something pop up on the screen. It said Simmons alert…seek shelter,” one student said. “We barricaded the door with chairs, we shut off the lights, shut off the projector and we all got into the front of the classroom and hid together.”

Emmanuel College and the Winsor School also issued a shelter-in-place order.

Boston police and heavily-armed SWAT teams could be seen sweeping the campus. No evidence of shots being fired was discovered, according to officials.

Simmons declared the emergency situation over around 3:20 p.m. and the lockdown was lifted.

The popping of balloons were part of an organized activity on campus, according to police.

Many students, in tears, could be seen phoning and texting their parents.

Simmons has since said it has “returned to normal activities.”

An investigation into the incident is ongoing.

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