Several people were shot at a Maryland high school on Tuesday, local news media reported, and school officials confirmed the campus was on lockdown and the incident had been "contained."
Multiple people were shot and their condition was not yet clear, ABC News reported, citing the St. Mary's County sheriff.
"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.
The violence was the latest in a decades-long series of shootings at U.S. schools and colleges, coming a little more than a month after 17 students and faculty were killed in a rampage at a Florida high school.
The sheriff's office confirmed the incident at Great Mills High School and urged parents in a Twitter post not to approach the campus.
Agents from the Federal Bureau of Investigation and the Bureau of Alcohol, Tobacco, Firearms and Explosives were heading to the school, the agencies said.
Great Mills High School is in St. Mary's County, which is about 70 miles (110 km) south of Washington.
The shooting occurred amid a re-energized national debate over school shootings in the United States following the attack on Feb. 14 at Marjory Stoneman Douglas High School in Parkland, Florida. It was the deadliest mass shooting at a U.S. high school.
"You never think it’ll be your school and then it is," Mollie Davis wrote on Twitter. "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.
Emma Gonzalez, a senior at Stoneman Douglas High School who survived last month's shootings, wrote on Twitter, "We are here for you, students of Great Mills, together we can stop this from ever happening again."
The shooting came four days before the March For Our Lives - partly organized by student survivors of the Parkland rampage - takes place in Washington to urge lawmakers 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.