A Colombian Air Force aircraft crashed on Monday morning in Puerto Leguizamo, rural southern Colombia, officials said.
Officials said on Monday that as many as 48 survivors had been found.
A military source told AFP that 80 people may have been killed, although there was no official toll.
However, Pedro Sanchez, the country’s defence minister, said the Hercules aircraft was carrying two platoons.
According to the military chief, a deployment is already underway in the area to assist the injured.
"With deep sorrow, I report that a Hercules aircraft from our Colombian Air Force suffered a tragic accident while taking off from Puerto Leguizamo (Putumayo), when it was transporting troops," Sanchez wrote on X.
While authorities mobilise to respond to the accident and determine its cause, the Defence Ministry has activated all protocols to assist victims and their families.
"I express my most sincere condolences to the families of those affected and, out of respect for their grief, I urge avoiding speculation until official information is available," Sanchez added.
The Hercules aircraft went down shortly after departure from Puerto Leguizamo, near the southern border with Ecuador, strewing burning wreckage on the jungle floor.
The troubled border area has been the scene of heavy military activity in recent weeks, as the Colombian and Ecuadoran militaries try to tackle drug-running cartels and militias. The toll remained unclear.
Images from the scene showed civilians clambering around the broken tail of the aircraft, marked FAC 1016, as smoke and flames billowed above the trees.
General Carlos Fernando Silva Rueda said that 114 troops were aboard and 11 crew.
They had been travelling between Puerto Leguizamo and another Amazon outpost nearby.
The crash is the second by a C-130 Hercules aircraft in South America in under a month.
A Bolivian military cargo plane carrying banknotes crashed while landing near La Paz on February 27, leaving at least 24 people dead.
The Hercules is a four-engine turboprop plane built by Lockheed Martin.
Renowned for its ability to operate from makeshift airstrips, it is widely used by militaries worldwide and can carry everything from troops to vehicles.
