Authorities said the DC-9 Intercontinental airliner exploded in mid-air, but witnesses in the town of Maria La Baja, 500 miles north-west of Bogota, said it plummeted without lights, slammed into an embankment and then toppled into a lagoon.
Erika Delgado, who was travelling with her parents and a younger brother from Bogota to the Caribbean resort city of Cartagena, was taken to hospital in shock and with a broken arm. She was reported to be "in good condition, conscious" and waiting for family members.
One farmer said he heard cries for help and found the girl on a mound of seaweed, which had broken her fall. Farmers said she told them her mother had shoved her out of the plane as it broke up and burst into flames.
As day broke, rescue workers converged on the swamp and pulled out 32 bodies, including those of the pilot and co-pilot. The murky waters may have pulled some bodies downstream and towards the Caribbean.
Rescuers were searching the swamp in small canoes using lanterns and portable generators in the hope of finding passengers. Navy boats were watching the stream's mouth.
The blast was reported by the pilot of an aircraft flying near by. The airliner was approaching Cartagena airport when the pilot asked for authorisation to descend from 18,000ft to 14,000ft - the last communication received from the control tower.
Farmer Argemiro Vergara saw the plane engulfed in flames some 900ft in the air before it plunged towards a lagoon and broke in two.
The aviation authority was reluctant to comment on the possibility of a terrorist attack. "Any judgement which we make immediately would be premature, irresponsible and not serious," said Alvaro Raad Gomez, authority director.
Aviation authorities sent a delegation to investigate the causes of the crash and to seek the plane's "black box" cockpit voice and flight recorders.
International airline passenger and pilots groups have repeatedly criticised Colombia's safety record, saying it is one of the world's most dangerous countries to fly in because of deficient air-traffic control, poor navigational aids and constant security violations.
The crash is the most serious air accident in Colombia since 19 May 1993, when a SAM Airlines Boeing-727 jet crashed into a mountain near the city of Medellin, killing all 132 people aboard.
There have since been several smaller crashes involving regional flights, with 11 people killed in May 1994 and seven in April 1994.