CHARLESTON, S.C. — A white gunman opened fire Wednesday night at a historic black church in downtown Charleston, S.C., killing nine people before fleeing and setting off an overnight manhunt, the police said.

At a news conference with Charleston’s mayor early Thursday, the police chief, Greg Mullen, called the shooting a hate crime.

“It is unfathomable that somebody in today’s society would walk into a church while they are having a prayer meeting and take their lives,” he said.

The police said the gunman walked into the historic Emanuel African Methodist Episcopal Church around 9 p.m. and began shooting.