A Colombian military transport plane with 121 people on board, mostly soldiers, crashed shortly after takeoff in the country’s south, killing at least 66 people, authorities said.

The defence minister, Pedro Sánchez, said the accident happened as the Lockheed Martin Hercules C-130 plane was taking off from Puerto Leguízamo, deep in Colombia’s southern Amazon region, on the border with Peru, as it transported troops from the armed forces.

Images shared online by Colombian media outlets showed a black cloud of smoke rising from a field where the plane crashed and a truck with soldiers rushing to the site.

The air force said in a statement that at least 77 people were rescued from the crash site with injuries. A spokesman from the defence ministry said that officials are still investigating the final number of fatalities.

Media outlets shared videos of soldiers being rushed from the site on motorcycles driven by local residents, while another group of residents tried to put out the fire that the plane crash had created in a field surrounded by dense foliage.

Carlos Fernando Silva, the commander of Colombia’s air force, said details of the crash were not yet known, “except that the plane had a problem and went down about two kilometres from the airport”.

Gustavo Petro, the Colombian president, described the crash as a “horrific accident that should never have happened”.

In a lengthy post, apparently attempting to pre-empt potential criticism, Petro said he had been trying to renew the military fleet for years but has been hindered by “bureaucratic difficulties”.

“If the civil or military administrative officials are not up to this challenge, they must be removed,” said Petro.

The leading candidates for the Colombian presidency – the first round of which will take place in late May, when Petro will not run as there is no re-election – also posted messages mourning the tragedy and calling for investigations into its causes.

Sánchez said rescue teams had been sent to the site of the crash and that the cause of the accident still had not been determined. Officials said two planes, with 74 beds, had been sent to the area to fly the injured back to hospitals in the capital, Bogota, and elsewhere.

“This event is profoundly painful for the country,” Sánchez wrote. “We hope that our prayers can help to relieve some of the pain.”

Sánchez later said: “The aircraft was in airworthy condition and the crew was duly qualified.”

The minister added that, while the causes are still under investigation, it is already possible to rule out that the crash was caused by an attack from any of the numerous armed groups that plague Colombia.

A spokesperson for Lockheed Martin said the company was committed to helping Colombia as it investigates the incident.

Hercules C-130 planes were first launched in the 1950s and Colombia acquired its first models in the late 1960s. It has more recently modernised some older C-130s with newer models sent from the US under a provision that allows for the transfer of used or surplus military equipment. Hercules C-130s are frequently used in Colombia to transport troops as part of the military’s operations amid a six-decade-long internal conflict that has claimed more than 450,000 lives.

The tail number of the plane that crashed on Monday matches that of the first of three planes delivered by the US to Colombia in recent years.

At the end of February, another Hercules C-130 belonging to the Bolivian air force crashed in the populous city of El Alto, barely missing a residential block, killing more than 20 people and injuring another 30.