Three people have been shot and injured at a high school in the US state of Maryland, local police say.

Gunfire broke out on Tuesday morning at Great Mills High School in St Mary's County, about 104km south-east of Washington DC.

St Mary's County Sheriff's Office says the incident has been contained. According reports, the attacker was shot by a school security officer.

It comes a month after a high school shooter killed 17 in Parkland, Florida.

According to sheriff's office spokeswoman Cpl Julie Yingling, the three people who were shot included the shooter.

All three people were taken to hospital. None are thought to have life-threatening injuries.

WJLA News reports that the shooter was "taken down" by a school security officer after the incident began.

"There has been an incident at Great Mills High School", the St Mary's County Sheriff wrote on Twitter.

"Parents please DO NOT respond to the school," officials added, telling parents to report to nearby Leonardtown High School School to be reunited with their children.

Some 1,600 students attend the school in the community of Great Mills near the Chesapeake Bay.

The shooting happened early in the morning as classes were first getting started, a sheriff's spokeswoman said.

"There has been a tragic shooting at Great Mills High School," the school district later confirmed in a statement on Twitter.

"The St Mary's County Sheriff is on the scene and the event is contained," the district's statement added.

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