Updated
A student has shot and critically injured two fellow students at a Maryland high school before a campus security officer ended the attack by injuring the shooter, a law enforcement official said.
The shooter shot a male and a female student at Great Mills High School in St Mary's County and was then injured by the campus security officer, county Sheriff Timothy Cameron told MSNBC.
All three were in critical condition at hospitals.
It was not clear whether the student shooter was shot by the security officer or injured in another fashion.
The reason for the shooting was unclear, Mr Cameron said, adding: "We don't know the relationship; we don't know the motivation."
Federal investigators from the Bureau of Alcohol, Tobacco, Firearms and Explosives were heading to the school, the agency said.
The shooting occurred amid a re-energised national debate over school shootings in the United States following an attack on February 14 at Marjory Stoneman Douglas High School in Parkland, Florida, where a gunman killed 17 students and staff.
"Please pray for us. There was a loud sound and everyone started screaming and running," a young woman named Mollie Davis, who identified herself as a student at Great Mills High School, posted on Twitter.
"You never think it'll be your school and then it is.
"Great Mills is a wonderful school and somewhere I am proud to go. Why us?"
Following the shooting, she exchanged messages on Twitter with students from Stoneman Douglas High School, saying their activism had inspired her to spearhead a walkout against gun violence at her school.
A few Parkland students expressed their sympathy and told her to be safe.
The shooting came four days before the March For Our Lives — partly organised by student survivors of the Parkland rampage — takes place in Washington to urge politicians to pass tighter gun control laws.
A student who said his name was Jonathan Freese said in a telephone interview on CNN that he had been on lockdown with classmates for nearly an hour, but he did not hear gunshots himself.
The interview ended as police came to his classroom door.
Maryland Governor Larry Hogan said he was monitoring events at the school.
"Our prayers are with students, school personnel, and first responders," he said in a statement.
Great Mills is a town about 110 kilometres south of Washington.
Reuters
Topics: law-crime-and-justice, united-states
First posted