Thirteen people were injured - including deputies, inmates and a firefighter - in Friday night's blaze in Bakersville, about 40 miles northeast of Asheville near the Tennessee state line.
The fire's cause hadn't been determined Saturday, but Mitchell County Sheriff Ken Fox said there didn't appear to have been foul play.
Investigators said the fire likely began in a ground-floor storage room containing wiring and an electric heater.
At the time of the fire, the jail held 17 inmates - some serving time for misdemeanors and others awaiting trial.
"The inmates were incarcerated for various reasons, but they're still human beings and noone deserves to die like this," Mark Broadway, the public information officer for Mitchell County, said to CBS News.
The fire in the two-story brick and wood building was discovered by a jailer about 10 p.m. Friday, Fox said. The officer and an inmate trustee worked to rescue the other inmates, but the heavy smoke forced them out of the building, the sheriff said. Two deputies were able to free eight inmates on the ground floor.
Seven of the dead inmates were trapped inside an upstairs cell and the eighth was in a ground-floor holding area, Fox said. They all appeared to have died from smoke inhalation, he said.
"You don't know what to say," Fox told reporters, adding that he knew some of the inmates personally. "You can't find the words. It's just tragic."
The four cells in the 1950s-era jail had to be opened one at a time with keys, Fox said. There were no sprinklers in the jail, he said. It was not immediately clear whether smoke detectors sounded.
About 100 firefighters from four counties extinguished the fire by 11:30 p.m., said Mark Broadway, a county spokesman.
On Saturday, mourners left bundles of flowers near the burned jail in downtown Bakersville, a town of 300 people.
"This is a very close-knit type community," said Tammy Rousseau, who with her 10-year-old daughter dropped off a bouquet of eight carnations, one for each inmate who died.
Rousseau said she believed the dead inmates included "a lot of young people who weren't in there because they had committed major crimes. They were trying to turn their lives around."
Authorities identified the dead inmates as Edmond Banks, 46; Danny Johnson, 42; Jesse Davis, 27; Jeremiah Presnell, 20; Jason Boston, 27; Joey Grindstaff, 23; Tywain Neal, 28; and Mark Thomas, 20. Their hometowns were not released.