Four young children have been found alive after more than a month wandering the Amazon jungle, according to Colombia's President Gustavo Petro.

"A joy for the whole country! The four children who were lost 40 days ago in the Colombian jungle were found alive," Petro tweeted on Friday, attaching a image that seems to show search crews treating the children in a forest clearing.

The children, who appear gaunt in the photos, are being evaluated by doctors and will be evacuated for medical treatment.

Lesly Jacobombaire Mucutuy, age 13, Soleiny Jacobombaire Mucutuy, 9, Tien Ranoque Mucutuy, 4, and infant Cristin Ranoque Mucutuy were stranded in the jungle on May 1, the only survivors of a deadly plane crash.

Their mother, Magdalena Mucutuy Valencia, was killed in the crash along with two other adult passengers: pilot Hernando Murcia Morales and Yarupari indigenous leader Herman Mendoza Hernández.

The children's subsequent disappearance into the deep forest galvanized a massive military-led search operation involving over a hundred Colombian special forces troops and over 70 indigenous scouts combing the area.

For weeks, the search turned up only tantalizing clues, including footprints, a dirty diaper and a bottle. Family members said the oldest child had some experience in the forest, but hopes waned as the weeks went on.

Indigenous leader Lucho Acosta, the coordinator of indigenous scouts, credited the "extra effort" of search and rescue teams and local authorities to find the children in a statement on Friday.

"They all added a little effort so that this Operation Hope could be successful, and we can hope the kids will emerge alive and stronger than before. We have been hoping together with the strength of our ancestors, and our strength prevailed," he said.

"We never stopped looking for them until the miracle came," the Colombian Defense Ministry tweeted.

During a press conference Friday evening, Petro said the children would receive immediate medical evaluation and treatment, and that he hoped to speak with them on Saturday.

"The most important thing now is what the doctors say, they have been lost for 40 days, their health condition must have been stressed. We need to check their mental state too," he said.

"They will receive medical treatment and depending on what the doctors say they might be transferred to Bogota or Villavicencio. I'm going to try speak with them tomorrow," he said.

Petro, who was previously forced to backtrack after mistakenly tweeting that they had been found last month, described the children's 40-day saga as "a remarkable testament of survival."

"These are the children of peace and the children of Colombia," he said.