As many as 50 people may have survived when the Hercules aircraft went down shortly after departure from Puerto Leguizamo, near the southern border with Ecuador, a military source said.

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 cause of the crash was not immediately known. State broadcaster RCN broadcast images of a badly damaged fuselage aflame in a forest clearing.

Defense Minister Pedro Sanchez expressed "deep sorrow" at the accident.

"Military units are already at the scene," Sanchez posted on social media, adding that "the number of victims and the causes of the crash have not yet been confirmed."

"It is a deeply painful event for the country. May our prayers bring some measure of comfort," said Sanchez.

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 around the world and can carry everything from troops to vehicles.