Two students at a Maryland high school were shot Tuesday after a classmate opened fire in the hallway just before the start of classes, authorities said.
Great Mills High School remained on lockdown after the shooting was "contained" when a school resource officer "engaged" the gunman, St. Mary's County Sheriff Tim Cameron told NBC Washington.
The chaos unfolded before 8 a.m. ET when the gunman walked into the 1,600-student school and fired a round at a female student, also hitting a male student.
The school resource officer was alerted to the gunfire and "quickly" confronted the gunman, according to Cameron said.
The officer fired "at least a round at the shooter, and I believe the shooter also fired a round," Cameron said, adding, "This is your worst nightmare."
The gunman and the female victim were hospitalized and listed in critical condition. The male victim was critically injured but stable. The officer was not wounded. All high schools in St. Mary's County are staffed with an armed deputy sheriff who works as a school resource officer.
Agents with the Bureau of Alcohol, Tobacco, Firearms and Explosives also responded to the scene, which is around 70 miles south of Washington.
Students were taken by bus to a nearby high school to be reunited with panicked parents.
Terrence Rhames, a senior at Great Mills, said he and his friends were talking before class when they heard the pop of a loud gunshot.
"I heard one shot and when we ran, we saw a teacher and he was looking at us with a confused look," Rhames said. "We were trying to figure out if this is real."
He said students raced for the exits and called their parents.
"It was just shocking. You hear about shootings you never think would happen to you," Rhames said.
The incident came ahead of Saturday's national March For Our Lives rally against gun violence following the mass shooting at Parkland, Florida, high school last month.
Students at Great Mills High School participated in last week's National School Walkout that honored the 17 victims of the Parkland shooting.
Emma González, a Parkland senior and activist, tweeted to Great Mills students on Tuesday morning that "we are Here for you."
House Minority Whip Steny Hoyer, D-Md., told NBC Washington that he was "sickened" to hear of another school shooting, this time in his district.
Across the country, "we've had 16 school shootings since the beginning of the year, just about one a week," Hoyer said. "It's unacceptable. We need to take action."
The White House this month said it will propose funding firearms training for school personnel and bolster firearm background checks, but steered clear of a previous idea floated by President Donald Trump to raise the minimum legal age to buy semiautomatic weapons from 18 to 21.
The state of Maryland prohibits anyone under the age of 21 from having a gun.
