Nashville’s police chief has said his officers are investigating if gender was a motive of a transgender school shooter.

Audrey Hale, 28, a former pupil at The Covenant School killed three children and three staff members during a carefully- planned shooting spree on Monday morning.

John Drake, the city's police chief, said the shooter "identified as transgender" and revealed that the shooter had made a manifesto, drawn a detailed map of the school and conducted surveillance of the building before carrying out the massacre.

Asked whether Hale's gender identity may have been a factor, Mr Drake said: "There is some theory to that, we're investigating all the leads."

The fee-paying Covenant School is affiliated with the evangelical Presbyterian Church in America, an evangelical religion which broke away from the larger Presbyterian organisation.

In 2020, the Presbyterian Church in America spoke of the "sinfulness" of transgender and homosexual desire and conduct, according to the New York Times.

Mr Drake said investigators believe Hale had "some resentment for having to go to that school" in an interview with Lester Holt on NBC Nightly News.

Hale had reportedly begun using male pronouns, including on Linkedin.

Hale carefully planned the attack and left behind a map charting the course but was shot dead before completing the rampage.

Before travelling to the school, Hale sent a series of messages to a friend on social media, warning that “something bad” was about to happen.

“This is my last goodbye. I love you. See you again in another life,” Hale told Averianna Patton, a former basketball teammate, News Channel 5 Nashville reported. “I’m planning to die today.”

Ms Patton, who called a suicide prevention helpline and then the police, replied: “Audrey! You have so much for life to live. I pray God keeps and covers you.”

The victims were identified as nine-year-old students Evelyn Dieckhaus, Hallie Scruggs and William Kinney.

The school’s head teacher, Katherine Koonce, 60; substitute teacher Cynthia Peak, 61; and a custodian, Mike Hill, 61, were also killed.

Police said Hale was a former student at the Presbyterian school, where fees are as much as $16,500 per year. It was unclear when Hale attended the school.

President Joe Biden called the shooting “sick” and reiterated his call for Congress to pass an assault weapons ban in the aftermath of the tragedy.

"We have to do more to stop gun violence. It's ripping our communities apart, it's ripping at the very soul of this nation," he said.

He said: "It's heartbreaking, a family's worst nightmare."

Residents in Nashville held multiple vigils Monday evening. At Belmont United Methodist Church, mourners held back tears as they sang, knelt in prayer and lit candles.

A contemporary Christian singer, Lauren Daigle, also put together a prayer vigil  after cancelling her concert at a venue in the Music City on Monday night.

The shooting in the affluent neighbourhood in Nashville, Tennessee is the latest in an ever-growing list of school shootings in America.

The country has experienced 129 mass shootings already this year, according to data from the non-profit Gun Violence Archive.

The Covenant School, a small school of around 200 children aged 4 to 12, as well as roughly 50 staff members, is attached to a church in southwest Nashville.

“Our community is heartbroken,” a statement from the school said. “We are grieving tremendous loss and are in shock coming out of the terror that shattered our school and church. We are focused on loving our students, our families, our faculty and staff and beginning the process of healing.”

Amid the chaos on the scene, a familiar ritual played out.

Terrified parents rushed to the school to learn their children’s fate, and a stunned community planned vigils for the victims.

Rachel Dibble, who was at a church acting as a reunification point for families, described the scene as one of "complete shock".

“People were involuntarily trembling,” she said. “The children … started their morning in their cute little uniforms, they probably had some Froot Loops and now their whole lives changed today.”

Monday's tragedy unfolded over roughly 14 minutes. Hale was heavily armed, with two assault-style weapons and a handgun.

The shooter gained entry to the school by shooting through a door on the side of the building and went from the first floor to the second floor firing multiple shots.

Police were called to reports of an active shooter at 10.13am.

By 10.27am, Hale had been shot dead by two officers in a five-member team on the second storey of the school.

The suspect was "prepared for a confrontation" with police and "prepared to do more harm" before being shot dead, Mr Drake said.

Police later discovered maps of the school drawn "in detail", noting the location of its security cameras and entrance points Hale appeared to have planned to target multiple locations.

"We have a manifesto, we have some writings that we’re going over that pertain to this date, the actual incident," the police chief said late on Monday.

He said police had spoken with the suspect’s father.

A LinkedIn profile reportedly belonging to the suspect lists Hale as an illustrator who attended the Nossi College of Art and Design in Tennessee.

Steve LaSuer, a teacher at Nossi who taught Hale around 2016, said he had been left aghast by the shooting.

"She just always was a kind of quiet girl but was very serious about her work," he told the New York Times.