A masked gunman opened fire at a Nashville church in Tennessee on Sunday, walking silently down the aisle as he shot unsuspecting congregants. At least one person was killed and seven others wounded, authorities said.

An usher confronted the shooter, who apparently shot himself in the struggle before he was arrested, police said.

The FBI said on Sunday night it has opened a civil rights investigation into the shooting at the Burnette Chapel Church of Christ.

No motive was immediately determined. Church members told investigators that the suspect had attended services a year or two ago, said Don Aaron, a spokesman for the Metro Nashville Police Department.

Nashville police did not immediately comment on several bizarre posts on the suspect's Facebook page in the hours before the shooting.

The gunman pulled into the church's parking lot as services were ending. He fatally shot a woman who was walking to her vehicle, then entered the rear of the church with two pistols and kept firing, hitting six people, Aaron said. Police said they later recovered another pistol and a rifle from the suspect's car.

Authorities identified the attacker as Emanuel Kidega Samson, 25, of Murfreesboro, who came to the United States from Sudan in 1996 and was a legal US resident.

It was unclear whether the self-inflicted wound to the chest was intentional, Aaron said.

The gunman was discharged hours later from Vanderbilt University Hospital but remained in police custody. The Metropolitan Nashville police tweeted Sunday night that Samson will be charged with one count of murder and that multiple “additional charges will be placed later.” He was ordered held without bail by a judicial commissioner.

Witness Minerva Rosa said the usher was “a hero.” “He's amazing,” said Rosa, a member of the church for eight years. “Without him, I think it could be worse.” The suspect said nothing as he fired. While the gunman made his way down the aisle, Rosa said, the pastor started shouting, “'Run! Run! Gunshots!'” Aaron called the usher, 22-year-old Robert Engle, “an extraordinarily brave individual.”

The woman who was killed in the parking lot was identified as Melanie Smith, 39, of Smyrna, Tennessee.

The gunman and six others were treated for gunshot wounds at nearby hospitals, along with Engle, who was pistol-whipped, Aaron said.

Among the wounded was Joey Spann, who is the church's pastor and is a Bible study teacher at Nashville Christian School.

After the attack, the nearby New Beautiful Gate Church opened its doors to Burnette Chapel churchgoers as they reunited with loved ones. New Beautiful Gate Pastor Michael Mosby said he is neighbours with Spann.

“As a pastor myself, you come with the expectation of sitting down and having a service and not thinking about what can happen around you,” Mosby said. “You never know who is going to come to the door or what reasons they would come to the door, come to your church and do something like that. We're always on guard.

We just thank God many more weren't hurt.” Forty-two people were at the church at the time of the shooting, and all victims were adults, Aaron said.

The small brick church describes itself on its website as a “friendly, Bible-based group of folks who love the Lord and are interested in spreading his word to those who are lost.” Photos on the church's Facebook page show a diverse congregation with people of various ages and ethnicities.

On Samson's Facebook page, a post in the hours before the shooting read, “Everything you've ever doubted or made to be believe as false, is real. & vice versa, B.” Another post read, “Become the creator instead of what's created . Whatever you say, goes.” And a third post read, “You are more than what they told us.”

Samson also posted several shirtless photos of himself flexing his muscles. In some he wears a tank top that reads “Beast Mode.” Nashville Mayor Megan Barry said in a statement that the shooting was “a terrible tragedy for our city.” She said her administration “will continue to work with community members to stop crime before it starts, encourage peaceful conflict resolution and promote non-violence.”