A small prayer circle forms nearby where police are responding to a shooting at the Emanuel AME Church in Charleston, South Carolina June 17, 2015. A gunman opened fire on Wednesday evening at the historic African-American church in downtown Charleston and was still at large, a US police official said, but there were no immediate confirmed reports of casualties. [Photo/Agencies]

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.

Following the attack on the church, Republican presidential candidate Jeb Bush, the former governor of Florida, canceled an appearance in Charleston that had been scheduled for Thursday morning.

"Governor Bush's thoughts and prayers are with the individuals and families affected by this tragedy," his campaign team said in a statement.

Local broadcaster WCSC reported the FBI was on the scene. The FBI could not be reached immediately for comment.

The website for the church said it has one of the largest and oldest black congregations in the South. It has its roots in the early 19th century, and the current building was built in 1891. It is considered a historically significant building, according to the National Park Service.