A six-year-old boy opened fire in an elementary school classroom in the eastern US state of Virginia on Friday, seriously injuring a teacher, police said.

No students were hurt in the incident at Richneck Elementary School in the coastal city of Newport News.

"The individual is a six-year-old student. He is right now in police custody," local police chief Steve Drew told a news conference, adding that "this was not an accidental shooting."

Police said that the victim was a teacher in her 30s and her injuries were believed to be life-threatening.

"I'm in shock, and I'm disheartened," said the city's superintendent of schools, George Parker.

"We need the community’s support to make sure that guns are not available to youth."

School shootings plague the United States, with recent tragedies including the killing last May of 19 children and two teachers in Uvalde, Texas, by an 18-year-old gunman.

There were an estimated 44,000 gun-related deaths in the United States last year, about half of them murder cases, accidents and self-defense, and half of them suicides, according to the Gun Violence Archive database.