"Nine brave, heroic, courageous firefighters of the city of Charleston have perished fighting fire in a most courageous and fearless manner, carrying out their duties," Charleston Mayor Joseph P. Riley said at a morning news conference. "To all of their loved ones, our heart goes out to them."
Two employees in the building were rescued from the blaze, which broke out at about 7 p.m. Monday in the Sofa Super Store and warehouse, Riley said.
Overnight, firefighters saluted as the bodies of their colleagues were taken from the warehouse.
"To lose nine is just a tragedy of immense proportions," Riley said. "To lose nine is just unbelievable."
Riley said the county coroner planned to disclose the names of the dead. The cause of the fire was under investigation, but Riley said arson was not suspected.
Riley said the blaze apparently started in a storage area and was unsure whether there were sprinklers in the building.
Charleston fire and rescue Lt. Chad Watson told CBS' The Early Show the store lacked a sprinkler system and that "it was just a matter of time" before the building collapsed from the heat of the fire.
Witnesses said the store's roof collapsed, throwing debris over about two-dozen rescue workers. Onlookers were hit with flying ash.
"It was like a 30-foot tornado of flames," said Mark Hilton, who was struck in his eye.
Eric Glover told CNN that he and a number of other firefighters were at a golf tournament to benefit the family of a firefighter who had recently died when they heard the call come over their scanners. By the time he arrived, he said, the roof had already collapsed.
"It all happened pretty fast. They didn't really have a chance," Glover said.
"You're always close to the guys because you spend a third of your life with these guys. Every third day you spend 24 hours there, so you get real close," he said.
Daniel Shahid, a salesman at a nearby car dealership, said firefighters came in asking for towels.
"The next thing you know, we were carrying hoses, directing traffic, everybody from the dealership," he said.
Shahid said he saw firefighters rescue four people from the building. "They were struggling. They were covered in black soot. They looked scared out of their minds," Shahid said.
Riley called the missing firefighters heroes.
"This is a profession that we must never take for granted," the mayor said. "There's a fire raging and they go toward it."
Update: A previous version of this story contained information from "The Early Show" in which CBS affiliate WCSC-TV correspondent Amanda Fitzpatrick reported residents had told her three residences near the warehouse had burned; it was later determined only the warehouse was affected.