Rescuers believe the four children, aged 13, nine, four and an 11-month-old baby, have been wondering through the jungle in the southern Caqueta department since the May 1 crash.

"The search efforts... have intensified in the last hours after finding new leads that could give indications about their whereabouts," said the armed forces in a statement.

Soldiers came across a "shelter built in an improvised way with sticks and branches," leading them to believe there are survivors.

In photographs released by the armed forces, scissors and a hair tie can be seen amongst branches on the jungle floor.

Previously, a baby's drinking bottle and a half-eaten piece of fruit had been found.

Between Monday and Tuesday, soldiers found the bodies of the pilot and two adults who had been traveling from a jungle location to San Jose del Guaviare, one of the main cities in Colombia's Amazon rainforest.

One of the dead passengers was the mother of the four children, whose surname is Ranoque Mucutuy and are from the Huitoto ethnicity.

Giant trees that can grow up to 40 meters tall, wild animals and heavy rainfall make the "Operation Hope" search difficult.

Three helicopters have been used to help, one of which blasted out a recorded message from the children's grandmother in the Huitoto language telling them to stop moving through the jungle.

Authorities have not indicated what caused the plane crash.

The pilot had reported problems with the engine just minutes before the airplane disappeared from radars, the Colombian diaster response body said.

It is a region with few roads that is also difficult to access by river, so locals usually choose to travel by airplane.