A heavily-armed 28-year-old woman killed three children and three staff at a private elementary school in Nashville on Monday before being shot dead by police, AFP reports.

Armed with at least two assault rifles and a handgun, the shooter entered the Christian Covenant School from a side door before opening fire, Nashville police spokesman Don Aaron told a press conference.

The assailant -- who police said was believed to be a former student at the school -- fired multiple shots as she advanced through the building.

Officers were on the scene within about 15 minutes of receiving the first emergency call around 10:00 a.m. local time, engaging the shooter who returned fire before she was shot dead, Aaron said.

The shooter was identified as Audrey Hale, 28, of Nashville, who identifies as transgender, Metropolitan Nashville Police Chief John Drake told reporters, according to NBC News.

A car near the shooting scene helped police determine who the shooter was.

“There was a vehicle that was nearby that gave us clues as to who she was,” Drake said, adding investigators were combing through Hale’s home.

US President Joe Biden described the latest shooting as "sick" and said gun violence was tearing the nation's "soul," as he urged Congress to pass a ban on the assault weapons commonly used in mass shootings.

"It's ripping our communities apart, ripping the soul of this nation, ripping at the very soul of the nation," he said.