The US Naval Academy in Annapolis, Maryland is on lockdown after reports of threats, official said, with reports saying that a former midshipman is involved.

"Naval Support Activity Annapolis, in coordination with local law enforcement, is currently responding to reports of threats made to the Naval Academy," The City Of Annapolis reported on Thursday.

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

Gunshots were heard inside Bancroft Hall, which houses the midshipmen, Fox News reported.

"The shooter is knocking on doors pretending to be a military policeman," it said, citing an official on the campus.