At least 34 people were killed when a Colombian Air Force plane carrying 125 people crashed just after takeoff in the south of the country, 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.

Maj Gen Carlos Fernando Silva, the chief of the Colombian air force, said the aircraft was carrying 11 air force members and 114 soldiers. He said that 48 injured people had been rescued but gave no figure for survivors or fatalities.

Gustavo Petro, the Colombian president, posted that there was at least one confirmed death, 77 people in hospital and “43 people whose status is to be established”.

The governor of the department of Putumayo, Jhon Gabriel Molina Acosta, told the television channel Caracol early in the evening that 34 deaths had been confirmed at that point, although the Colombian government has yet to officially verify the figure.

The mayor of Puerto Leguízamo, Emilio Augusto, told Radio Caracol that “medical capacity has been overwhelmed by the magnitude of the emergency”, and requested immediate support from the national and departmental governments to evacuate the injured.

The armed forces deployed seven aircraft to transport the injured and posted a video of some of them arriving in the capital, Bogotá. They were all on stretchers – most of them motionless – some with oxygen cylinders and covered with thermal blankets, and one conscious and even able to take a few steps.

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.

Images shared online by local media outlets show a black cloud of smoke rising from a field where the plane crashed, a truck with soldiers rushing to the site and civilians trying to extinguish the fire.

Sánchez did not specify the number of troops who were onboard the Hercules C-130. He said rescue teams had been sent to the site of the crash and that the cause of the accident still had not been determined.

“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.

The US defence company Lockheed Martin did not immediately respond to a request for comment.

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.