THREE people have been injured in a school shooting in Great Mills High School in southern Maryland.

A spokeswoman for the St Mary's County Sheriff's Office told NBC news the shooter was among the injured and all three had been taken to hospital. 

There condition and connection to the school is unknown.

County Sheriff Timothy K. Cameron said the shooter fired at a female victim at the beginning of the school day around 8am local time and was later confronted by a school resource officer. 

The school has described the incident as "tragic" and urged both parents and students to stay away while the building is in lockdown. 

The school reported a shooting on Tuesday, and authorities would say only that the situation had been contained at the time.

"There has been a shooting at Great Mills High School," the school district said in a tweet. "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 County Sheriff's Office confirmed that it was on the scene and urged parents to go to another local high school to reunite with their children. 

The Bureau of Alcohol, Tobacco and Firearms said special agents from Baltimore and Hyattsville were en route to the scene.

A school shooting last month in Parkland, Forida, resulted in 17 deaths and sparked a nationwide discussion over how to make schools safer. High school students across the nation held a walkout last week to press for safer schools, and marches are planned Saturday across the nation.