Authorities on Thursday captured the white suspect in a gun massacre at one of the oldest black churches in the United States, the latest deadly assault to feed simmering racial tensions.

Authorities on Thursday captured the white suspect in a gun massacre at one of the oldest black churches in the United States, the latest deadly assault to feed simmering racial tensions.

Police detained 21-year-old Dylann Roof, shown wearing the flags of defunct white supremacist regimes in pictures taken from social media, after nine churchgoers were shot dead during a Bible study class on Wednesday.

He was caught at a traffic stop in North Carolina and flown back just hours later to Charleston, South Carolina, the scene of the slaughter in the Emanuel African Methodist Episcopal Church.   

Television footage showed the slender suspect boarding a small aircraft with his hands tied and wearing a black-and-white horizontally striped prison uniform.

Booking photos released by Charleston County jail showed a sullen, boyish suspect with a pudding-bowl haircut.

The carnage was the worst at a US place of worship in decades and recalled the darkest periods of US history, in a church once burned to the ground after a failed slave revolt.

Charleston Police Chief Gregory Mullen said: "I do believe it was a hate crime."

A reported friend of the accused, 21-year-old Dalton Tyler, told ABC News that Roof had spoken in support of racial segregation and had "said he wanted to start a civil war."

In Washington, a clearly frustrated President Barack Obama said the "senseless murders" showed the United States will have to come to grips with its gun culture.

"At some point, we as a country will have to reckon with the fact that this type of mass violence does not happen in other advanced countries," Obama said.

Members of the historic church's mainly black congregation, many of them elderly, had gathered Wednesday evening for a Bible study meeting when the shooter walked into the building, sat for about an hour, then opened fire.

Sylvia Johnson, a relative of one of the victims, told CNN a survivor had told her that the gunman had made a racist rant during the attack.

Johnson said one of the victims tried to talk the shooter out of more killings after he opened fire.

"He said 'No, you've raped our women and you're taking over the country. I have to do what I have to do,'" she told CNN.

Johnson also said the shooter told the victims he left survivors so they could tell the story of the shooting.

Three men and six women were killed, and more people were wounded. Among the dead was the church's pastor, 41-year-old Clementa Pinckney, who also was a Democratic state senator known to Obama.