Colombian Defence Minister Pedro Sánchez said the Lockheed Martin-built Hercules C-130 transport plane had suffered “a tragic accident while it was taking off from Puerto Leguízamo, transporting troops of our security forces”.
He described the incident near the border with Peru as “deeply sad for the country”.
Ammunition being carried on board detonated as a result of a fire on the aircraft, Sanchez later said.
A military source told AFP that 58 soldiers had died, along with six air force personnel and two police officers.
Two military sources also told Reuters that 66 people had died.
The incident was one of the deadliest accidents in recent history for Colombia’s Air Force.
Images shared by local media show a plume of smoke rising from the site and trucks carrying soldiers heading to the area.
Footage on local news sites also appears to show locals transporting what seem to be injured soldiers from the accident site to hospitals on the back of small motorbikes.
President Gustavo Petro wrote on X that “this horrendous accident … should not have happened”.
In the lengthy post, he also blamed “bureaucratic problems” for holding up his plans to modernise the armed forces’ equipment and their aircraft.
“I will allow no further delays, the lives of our young people are at stake,” he wrote, without clarifying what may have caused the accident.