A fire at a prison in southeast of the Chilean capital, Santiago de Chile, has killed at least 81 people.
Some reports suggested the fire was deliberately started on Wednesday, during a fight between inmates in one of the crowded San Miguel prison's five towers.
Al Jazeera's Pablo Fernandez, reporting from Santiago, said relatives of the prisoners denied that claim, saying instead that the fire started after an electric fault.
"Relatives of the inmates are very angry," he said.
"They deny the version that this was started by a riot. They say that there was a short circuit, and that the authorities always blamed the fire on the inmates."
Fernandez said relatives had received phone calls from family members inside the prison, using illegal mobile phones, informing them of what had happened.
However, authorities were denying their claims.
According to the AFP news agency, citing officals, the fire started around 08:30 GMT on the fourth story of the penitentiary during a fight among inmates in a ward reserved for low-risk prisoners, most with only a single conviction.
Prisoners lit their mattresses on fire, causing the blaze to sweep through the ward in "less than three minutes," an inmate told AFP on condition of anonymity.
Most of those killed were believed to have died from smoke inhalation, authorities said.
Sebastian Pinera, the president, called the blaze "a hugely painful tragedy."
"The situation in our prison system cannot hold out any longer," he said, citing chronic overcrowding in the country's jails.
Felipe Bulnes, the justice minister, said the prison housed 1,960 inmates, nearly twice the 1,100 capacity.
Police Colonel Jaime Concha said 14 inmates were also injured in the fire, which broke out before dawn on Wednesday.
"We don't yet have the identities" of the deceased inmates, he said.
Prison officials said one firefighter was among the dead.
Television footage showed flames engulfing the jail and black smoke billowing from the building.
Some inmates waved their hands through bars in one wing of the prison, as family members cried and screamed, imploring police to let them into the prison to rescue their relatives.
Wednesday is visiting day, which meant many families had already planned to head to the prison.
Anxious to find their loved ones, some climbed onto the prison fence, shouting out inmates' names at the burning building.
Some relatives of inmates told state television that prison police had closed the gates to the prison, impeding access for firemen.
Jaime Concha, the police operations director, insisted that police had acted quickly.