At least 49 prisoners were dead and many more were injured during the early hours of Tuesday, 28 June, while trying to escape from a prison in the city of Tulua in southwestern Colombia, AFP reported.
A spokesperson for the National Penitentiary and Prison Institute said that the death count was preliminary and "may change."
Inmates tried to escape following a fire, Caracol Radio quoted authorities as saying.
A prison cell that normally hosts around 180 people was set ablaze in Colombia.
The head of the government's prison agency, General Tito Castellanos, said that some mattresses were set alight by the inmates "without considering the consequences of how it was going to affect them," BBC reported.
"It created a cascade effect that spread to virtually the whole block," he added.
"The guards, using fire extinguishers and other items, managed to evacuate the majority of the inmates, but unfortunately the outcome was 49 dead and 30 injured," he said.
Outgoing President Ivan Duque expressed solidarity with the relatives of the victims via a tweet.
"We regret the events that occurred in the prison in Tulua, Valle del Cauca," he wrote.
"I have given instructions to clarify this terrible situation. My solidarity is with the families of the victims," he added.
(With inputs from BBC and AFP.)