At least 66 members of Colombia's armed forces were killed when a military aircraft crashed shortly after take-off in the south of the country early on Monday, authorities said.

Colombian Chief of Defense Hugo Alejandro Lopez Barreto said that "sadly, as a consequence of this tragic accident, 66 of our armed forces members died."

The majority of those killed were members of the army, while members of the Colombian Aerospace Force and two members of the national police force also died, he said.

So far, 57 people have been brought to the hospital with serious injuries, according to the defense chief.

Lopez Barreto said a total of 128 people, including 11 crew members, were aboard the aircraft, after authorities initially said 125 were on board.

"At present, we have no information or evidence to suggest that this may have been an attack carried out by an illegal armed group," he said.

Colombia has long struggled with internal conflict. Following decades of warfare involving left-wing guerrilla groups, the country is also struggling to contain drug-related crime.

The C-130 Hercules aircraft was traveling from Puerto Leguízamo to Puerto Asís in the Putumayo Department, near the border with Peru, when it crashed shortly after takeoff.

The cause of the accident remains unclear.

Videos showing clouds of grey smoke and wreckage have been published on social media.