The US Naval Academy in Annapolis, Maryland, was locked down Thursday after reports that a dismissed midshipman returned to campus with a weapon and opened fire.

Gunfire was heard inside Bancroft Hall, the academy’s massive dormitory housing more than 1,600 midshipmen, Fox News reported, citing Naval Academy sources. The alleged shooter was said to have knocked on doors while posing as a military policeman.

Video showed one individual being transferred from an ambulance to a medevac helicopter on campus, according to Fox News.

The academy in Annapolis was working with local law enforcement to respond to the reports of threats, Lt. Naweed Lemar, the spokesperson for the base that hosts the academy, said in a statement.

“The base is on lockdown out of an abundance of caution,” he said. “This is a developing situation and we will provide updates as they become available.”

Police were near Bancroft Hall, which houses midshipmen in its more than 1,600 dorm rooms. It is considered the biggest single college dormitory in the world, according to the school’s website.

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