US police have arrested a 21-year-old white gunman suspected of killing nine people in one of the nation’s oldest black churches in Charleston.

The carnage at the Emanuel African Methodist Episcopal Church in the southeastern US city in South Carolina was one of the worst attacks on a place of worship in the country in decades, and comes at a time of lingering racial tensions nationwide.

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Dylann Roof – a slight man with a bowl haircut and a youthful face – was taken into custody on Thursday in neighbouring North Carolina, about a four-hour drive from the scene of the shooting, Charleston Police Chief Gregory Mullen said.

“I do believe it was a hate crime,” Mullen said.

A clearly frustrated President Barack Obama said the incident showed that the country needed to look again at how violent people get their hands on guns, calling the killings “senseless”.

“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 at the White House.

“It doesn’t happen in other places with this kind of frequency. And it is in our power to do something about it.”

Members of the church’s mainly black congregation had gathered on Wednesday evening for a Bible study meeting when the shooter walked into the building, sat for about an hour and then opened fire, 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.

Side streets around the church were sealed off with yellow crime scene tape on Thursday, and a police officer told AFP some of the bodies of the victims were still inside.

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 in with local police.

“The fact that this took place in a black church obviously also raises questions about a dark part of our history,” Obama said.

A picture on Roof’s Facebook page showed him wearing a black jacket with patches emblazoned with the flags of apartheid-era South African and white minority-ruled Rhodesia, now Zimbabwe.

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

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.

– AAP