A male student opened fire with a handgun in the hallway of a southern Maryland high school on Tuesday, the local sheriff said, critically injuring two students and exchanging gunfire with an officer stationed at the school.

The shooting suspect, who has not been named, was confirmed dead at 10:41am, said Sheriff Timothy K Cameron of St Mary's County, adding that it was not immediately clear whether the officer's round of gunfire struck the suspect.

The sheriff's office said it received a call of shots fired just before 8am at Great Mills High School in Great Mills, about 100km southeast of Washington.

Cameron said the school resource officer was alerted to the gunfire: "He pursued the shooter, engaged the shooter, during which that engagement, he fired a round at the shooter simultaneously the shooter fired a round as well."

Cameron said the officer, whom he did not identify, was not injured during the shooting. He said a male student was transported to a hospital in a stable condition, and a female student was transported to a shock trauma facility, where she was in a critical condition. Neither of the victims were identified.