CHARLESTON: US police on Thursday reportedly captured a 21-year-old white gunman who killed nine people at a prayer meeting in one of the nation's oldest black churches in Charleston, an attack being probed as a hate crime.

The shooting at the Emanuel African Methodist Episcopal Church in the southeastern US city was one of the worst attacks on a place of worship in the country in recent years, and comes at a time of lingering racial tensions.

The suspect — identified as Dylann Roof of Columbia, South Carolina — has been taken into custody in neighboring North Carolina, CNN and two local television stations reported, citing law enforcement sources.

Churchgoers had gathered Wednesday evening when the shooter walked into the building, sat in the congregation for about an hour and then opened fire, Charleston Police Chief Gregory Mullen said.

Three men and six women were killed, and several other people were wounded.

Among the dead was the church's pastor Clementa Pinckney, who was also a Democratic state senator.

“At this point, we have nine victims in this hideous crime that has been committed,” Mullen told journalists.

"I do believe it was a hate crime."

Police released photos of Roof — a slender white man with dark blond or brown hair in a distinctive bowl-type haircut and wearing a grey sweater.

“He obviously is extremely dangerous,” Mullen said.

The shooting comes at a time of heightened racial tensions in America, after several high-profile killings of unarmed black men at the hands of white police in recent months led to protests and a national debate on race.

A Justice Department spokesperson said a hate crimes probe had been opened, with FBI agents working in tandem with local police.

“My heart is breaking for Charleston and South Carolina,” said Senator Tim Scott of South Carolina, one of only two African Americans in the Senate.

'Absolutely bizarre'

Jim Curley, owner of AC's Bar & Grill, which is located a few blocks from the church, said locals were shocked anyone would carry out an attack in the popular tourist area.

“This is absolutely bizarre,” Curley told AFP. “This is really completely out of the blue... We have no idea what the motivation is." The incident once again highlights broad racial tensions that persist in many US communities, more than five decades after the Civil Rights Act outlawed racial and other forms of discrimination.

In April, in the neighboring city of North Charleston, a white police officer was charged after a video surfaced of him fatally shooting a fleeing black man in the back after a traffic stop.

But Curley said the neighborhood's residents typically get along fine.

“Generally, there's not a great deal of racial tension,” he said.

'Dastardly act'

Charleston is known locally as “The Holy City,” due to its large number of churches and historical mix of immigrant ethnic groups that brought a variety of creeds to the city on the Atlantic coast.

“People in prayer on a Wednesday evening. A ritual coming together, praying and worshipping God. To have an awful person come in and shoot them is, is inexplicable,” Mayor Joseph Riley said.

Dot Scott, the head of the local chapter of the National Association for the Advancement of Colored People (NAACP), said the shooter may not have drawn attention because of the church's location.

“It sits in an area that a lot of the tourists frequent. It's not out of the ordinary that folks just walk into the sanctuary and sit and listen to what's going on,” Scott told CNN.

Officials did not release detailed information about the victims, or say what kind of gun was used.

According to its website, the Emanuel African Methodist Episcopal Church is the oldest such church in America's southern states.

The church was founded in 1816 and in 1822 was investigated for its involvement with a planned slave revolt, the website states.

“The only reason someone can walk into church and shoot people praying is out of hate,” Riley said. “It is the most dastardly act that one can possibly imagine."

Republican presidential candidate Jeb Bush canceled campaign events that had been planned for Thursday in Charleston.

“Heartbreaking news from Charleston - my thoughts and prayers are with you all,” tweeted Democratic presidential candidate Hillary Clinton, who had been in Charleston earlier Wednesday.

The Charleston shooting is the latest on a long list of mass shootings in the United States.

The deadliest in recent years include the April 2007 Virginia Tech shooting, when 32 were killed, and the December 2012 Sandy Hook elementary school shootings in Newtown, Connecticut, when a total of 27 people died, including 20 children.

In August 2012, six people were shot dead at a Sikh temple in Wisconsin by a neo-Nazi US military veteran.

Charleston is famous for its cobblestone streets, Southern cuisine and nearby beaches and islands. The city is also known outside the United States for its namesake 1920s dance.

Earlier it had been reported that none of the victims from the shooting were immediately identified. But the Reverend Al Sharpton, the New York-based civil rights leader, said in a Tweet that the Reverend Clementa Pinckney, the church's pastor and a member of the state Senate, was among the fatalities.

The shooting occurred at the Emanuel AME Church in the historic centre of downtown Charleston around 9 pm (0100 GMT), according to Charleston Police Department spokesman Charles Francis.

After the shooting, a bomb threat was reported near the church, Charleston County Sheriff's Office spokesman Eric Watson said, and people who were gathered in the area were told by police to move back.

Chief Mullen told the press conference that the all-clear had been given after checks following the bomb threat.

A police chaplain was present at the scene of the shooting, and a helicopter with a searchlight hovered overhead as officers combed through the area.

Several men stood in a circle in front of a hotel near the church.

“We pray for the families, they've got a long road ahead of them,” Reverend James Johnson, a local civil rights activist, said during the impromptu prayer service.

Police took a man with a backpack and a camera into custody, but later said they were still searching for a suspect in the shooting.