Police in Charleston, South Carolina, are hunting a gunman who shot dead nine people at a church with a predominantly black congregation.
Officers said he burst in on a Bible study group at the historic Emanuel African Methodist Episcopal Church at abut 9pm.
Greg Mullen, the Charleston police chief, confirmed that nine people had died.
Worshippers embrace following a group prayer across the street from the scene of the shooting (AP)
"It will be investigated as a hate crime," he said.
He added that police were still hunting for the gunman three hours later.
"It is unfathomable that someone would walk into a church when people are having a prayer meeting and take their lives."
Earlier Joe Riley, mayor of Charleston, confirmed that had been fatalities.
Police close off a section of Calhoun Street near the Emanuel AME Church (AP)
"This is an unspeakable and heartbreaking tragedy in this most historic church, an evil and hateful person took the lives of citizens who had come to worship and pray together," he said.
Thomas Dixon, a local pastor, told CNN: "It's really bad. It's a very bad scene.
The scene minutes after a gunman opened fire on a church in Charleston
"Apparently the person just entered the church and opened fire.
"That part has not been fully articulated on what happened yet ... they are still looking for the suspect."
A helicopter hovered overhead as police sealed off streets around the church.
The website for the church said it has one of the largest and oldest black congregations in the region.
The church was built in 1891 and is considered a historically significant building, according to the National Park Service.
A small prayer circle forms close to the shooting at the Emanuel AME Church (AP)
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 southern city on the Atlantic coast.
Local reports said a Bible study group met on Wednesday evenings.
Local ministers comfort each other near the site of the shooting at the Emanuel African Methodist (AME) Episcopal Church (EPA)
Police briefly detained a man who matched the description of the gunman, however, he was identified as a local photographer and the search continued.
A group of 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.