UPDATED 12:00 p.m. ET: The shooter has been pronounced dead, CNN reported. St. Mary's County Sheriff Tim Cameron shared the news, adding that after engaging the shooter, the school resource officer ended the threat. The officer fired "at least a round at the shooter, and I believe the shooter also fired a round," Cameron said. The officer wasn't injured.

All St. Mary's County area high schools have one army deputy sheriff on staff, who works as a school resource officer.

UPDATED 10:21 a.m. ET: Three people have been injured at Great Mills High School, including the shooter, MSNBC reported. Per the St. Mary's County sheriff Tim Cameron, the shooter is in critical condition, a female student is in critical condition, and a male student is in critical but stable condition.

The sheriff also specified that a school resource officer "engaged" the shooter quickly after the shooting occurred. The school is now evacuating the students out of the high school and moving them to another location where they will meet with their parents.

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A Maryland high school was placed on lockdown on Tuesday morning following a shooting, according to local reports.

ABC 2 in Baltimore is reporting a shooting took place at Great Mills High School in St. Mary's County, Maryland. The school posted a short statement about the shooting on its website shortly before 9 a.m.

"There has been a Shooting at Great Mills High School," the statement said. "The school is on lock down the event is contained, the Sheriff's office is on the scene additional information to follow."

The St. Mary’s Sheriff’s Office sent out a tweet confirming an "incident" at the school on Tuesday. Police are asking parents of students at Great Mills to report to another local high school.

No other details are available as of yet.