Police and the ATF have responded to a shooting in a Maryland high school this morning, where at least three people have been injured, according to a CBS News report. Local police have called the situation “contained” but warn parents not to come to the school. Instead, they will bring students out to another high school in the district to reunite them with parents.

Details are understandably sketchy at the moment, of course:

A Maryland high school was on lockdown Tuesday morning after reports of a shooting, authorities said.

Police were at the scene at Great Mills High School in Great Mills, about 70 miles south of Washington.

Potential injuries were not immediately known and the St. Mary’s County Sheriff’s Office said in a statement that the incident was “contained” but parents should not go to the school.

Governor Larry Hogan put out a statement on Twitter that he would be “closely monitoring” the events at the school:

This CNN video shows the scope of the response, although it doesn’t show much more:

NBC Washington reports that at least “some of the injuries are critical,” and have already been taken to the hospital. Their live coverage is embedded below:

Bear in mind that initial reports are often inaccurate, and that details later emerge that either contradict or clarify initial impressions. We’ll keep updating this as solid developments emerge.

Update: The sheriff’s PIO told NBC that the incident involved a single male shooter who was a student at the school, who targeted a female student. The armed guard (school resource officer) at the school then engaged in a firefight with the shooter, critically wounding him, and a third student was injured. The shooter and intended target are both critically injured, and the third student is in critical but stable condition. So far, they are not releasing any information on the weapon itself.

Update: This points out the value of having armed resource officers on campus, at least when they are willing to respond. As the PIO pointed out, this could have been a lot worse, especially because the shooting took place in a crowded corridor.

Update: Added the note about the SRO to the headline, as that part of the story probably requires emphasis.

Update: The shooting suspect has died, according to the sheriff:

That may complicate efforts to determine the motive, but it shouldn’t impact other aspects of the investigation. The sheriff also explained the SRO’s actions:

A good guy with a gun stopped the bad guy with the gun.