The early morning blaze at San Miguel prison, which preliminary reports indicated may have been intentionally set, was the worst disaster in the history of Chile's penitentiary system, said Health Minister Jaime Manalich.
The fire began during fighting between inmates early and reached its maximum intensity in just three minutes, Interior Minister Rodribo Hinzpeter said. It was brought under control in three hours.
Police operations director Jaime Concha insisted police acted quickly despite coping with 1,900 inmates at the prison built for 700.
"The conditions that existed inside this prison are absolutely inhumane," said Chilean President Sebastian Pinera, who visited an emergency center where inmates were being treated for severe burns and smoke inhalation.
Chilean television broadcast spine-chilling audio and video from the prison fire, some of it shot by prisoners using illegal cell phones and sent to stations.
The state channel aired a recording of an inmate calling from inside the burning prison and pleading for help. Screams could be heard in the background. Other broadasts showed the smoked-filled prison tower and inmates shouting over and over again: "The doors!" and "We're burning!"
Private Mega TV broadcast a recording made by a prisoner of inmates in the burning tower screaming "Help! Help! Open the doors!"
Investigator Alejandro Pena said preliminary reports indicated the fire was set intentionally, but he didn't say by whom. An inmate told state television, however, that the fire began when a small stove fell during a fight.
Santiago region Gov. Fernando Echeverria said the official death toll was 81. By Wednesday evening, officials had identified 31 of the victims with many of the bodies unrecognizable. Officials said most will have to be identified by DNA.
Firefighters said they were alerted to the fire by a call from a cell phone inside the prison, a collection of cement towers that rises above a middle class neighborhood in Chile's capital.
A fire department communique said the first firefighters arrived on the scene nine minutes after the initial alarm at 5:48 a.m., and found a violent fire spread over a large part of the fourth floor of Tower 5. They cut through several locks, allowing them to save 60 inmates, it said.
Hundreds of anxious and angry relatives of inmates gathered in a chaotic scene outside the prison gates. Some waited six hours before officials read out the names of survivors - which people mistook for those of the dead.
There had been warnings of problems at the prison.
In October, Judge Ana Maria Arratia Valdebenito said that Tower 5, where the fire began, held 484 prisoners - more than 100 per floor.
National Human Rights Institute director Lorena Fries said the overcrowding in Chile's prison is a problem that has been noted by the United Nations. The country has "55,722 people in its prisons, which have a capacity to hold 31,576 inmates," she said.
Many of the inmates in the tower were first-time offenders. Among the dead was 22-year-old Bastean Arriagada, who was serving a 61-day sentence for selling pirated films.
Pedro Hernandez, who directs Chile's prison guards union, said there were only five guards to watch over the prisoners. Pinera, however, said there were six guards in the prison towers where the inmates are held, and 26 others stationed at the perimeter.
Some relatives of inmates told state TV that prison police initially closed the gates to firefighters, impeding efforts by 10 units to control the blaze.
"They wouldn't let the firefighters come in. The riot police came in first and began to beat us, and later the firefighters came in," an unidentified prisoner said in a call that was played on state TV. He didn't give his name, saying he feared retribution.
He said the guards "laughed and took photos with the cell phones of the inmates who were vomiting (from smoke) ... and didn't do anything." Officials evacuated prisoners from lower floors instead of those inmates who were dying, the prisoner said.
But Fire Department Cmdr. Jose Sanchez said it took 10 minutes for firefighters to enter the prison, blaming any delay on "the intense heat" they encountered, not on the guards.
While more than 200 inmates were moved to other areas of the prison, there were 147 others in the immediate area of the blaze, and many died of asphyxiation, the firefighters' statement said. It was supposed to be visitors' day at the prison, so many family members were already lining up outside when the fire broke out. Their anxiety spilled over when they learned that prisoners were killed. Some broke down in tears and screams, while others threw rocks at national prison police director Luis Masferrer as he read the survivors' names over a megaphone.
Manalich said 14 prisoners were badly burned, with uncertain fates. Two firefighters and three guards were less seriously hurt, authorities said.
A fire in a northern prison killed 26 people in 2001.