An armed student was killed in a school in Maryland in the United States on Tuesday after he opened fire on campus and injured two students. The shooter was killed in a gunfight with the school resource officer, St Mary’s County Sheriff Tim Cameron said, according to CNN.

MedStar St Mary’s Hospital said both students injured are in stable condition. The 16-year-old girl was in a critical condition earlier, but she was stabilised at the UM Prince George’s Hospital Center, NBC reported.

Authorities have not revealed the identity of the shooter yet.

“This is what we train for,” the sheriff said, according to The Baltimore Sun. “This is what we prepare for, and this is what we pray we never have to to, And on this day, we realised our worst nightmare that our greatest asset – our children – were attacked in a bastion of safety and security, one of our schools.”

County Spokesperson Tony Jones said the shooting occurred around 8 am. The school was locked down soon after the shooter opened fire, and students were evacuated.

This is the latest in a string of school shooting across the US this year. According to CNN, there have been 16 school shootings in 2018 alone, averaging to about 1.5 such incidents a week.

On March 8, a student was killed and another injured in a shooting at a high school in the city of Birmingham in Alabama. Just three weeks earlier, a 19-year-old gunman opened fire in a school in Florida’s Parkland on February 14, killing 17 people. Thousands of US students marched out of their classrooms through March to demand action against gun violence.