The discovery in recent days of small footprints in a southern jungle-covered part of Colombia has rekindled hope of finding alive four children who survived a small plane crash and went missing a month ago.

Searchers found footprints Tuesday about 3.2km northwest of where the plane crashed May 1 with three adults and four indigenous children aged 13, 9 and 4 and 11 months, Pedro Sánchez, commander of the Joint Command of Special Operations said in an interview with the Associated Press.

The searchers believe they were of the oldest child, a girl, and the new clue may indicate that the group has changed course.

More than 100 members of Colombia’s special forces and more than 70 indigenous people from the area have joined the search through the virgin jungle in the Colombia Amazon. Some soldiers have walked nearly 1500km or almost the distance from Lisbon to Paris, Sánchez said.

“We have a 100 per cent expectation of finding them alive,” Sánchez said but said the search is extremely difficult work. “It’s not like finding a needle in a haystack, it’s like finding a tiny flea in a huge rug that moves in unpredictable directions.”

Colombian President Gustavo Petro has said finding the children is a priority, and Sánchez said no deadline has been set for wrapping up the search.

Indigenous people arrive at the airport in San Jose del Guaviare, Colombia, to help search for four children missing after a plane crash. Photo / AP

“We found elements that are very complex to find in the jungle. For example, the lid of a baby bottle. If we’ve found that, why don’t we find the rest? Because the children are on the move,” Sánchez said.

General Pedro Sanchez, the commander of the joint command of special operations of the military forces, welcomes Indigenous people at the airport. Photo / AP

About two weeks after the crash, the remains of the aircraft were found along with the bodies of the pilot and two other adults travelling aboard. The children weren’t found, but there were clear indications they had survived the crash.

Searchers believe the children likely are still alive because otherwise animals would have been drawn to their remains, Sánchez said.

Special forces soldiers are working in rotations and must deal with up to 16 hours a day of rain that can wipe out any tracks of the children. They also must brave wild animals such as jaguars, ocelots, poisonous snakes and mosquitos that carry diseases, Sánchez said.

The soldiers also risk getting lost in the dense jungle, where visibility can be less than 20 metres.

“If they move more than 20 metres away, they can get lost,” Sánchez said.

The soldiers believe that the footprints found Tuesday are that of the 13-year-old girl based on their size.

The jungle areas that have been searched have been marked off with tape and whistles have been left in case the children come across those areas and can use them to call for help.

The search teams also have been blasting the area with recordings of the voice of the children’s grandmother, though heavy rains have been drowning out the sound, Sánchez said.

Among the clues that commandos have found over the past few weeks are a bottle, some towels, used diapers, some scissors and footprints in places relatively close to the place where the accident occurred. It has not been possible to establish whether the children abandoned those belongings intentionally to leave clues to those who are looking for them.

The accident occurred on the morning of May 1 after the pilot declared an emergency due to engine failure. The flight was going north from the town of Araracuara in the south and crashed about 175km from San Jose Del Guaviare.

- Eduardo Hernandez, AP