National Liberation Army (ELN) guerrillas handed over the group to a regional ICRC official in a rural area of San Pablo, not far from where the twin-engine Fokker 50 was forced to land after being commandeered Monday en route from the northeastern city of Bucaramanga to Bogota.
"We don't have their identities, but we know that they're well," said Rolin Wavre, the deputy Red Cross chief for Colombia.
There was no word on the fate of the remaining passengers and crew members.
Police searched the airstrip in Vijagual, 220 miles north of Bogota, on Tuesday, but all they found was an empty plane with its tires blown out. Pilots who flew over the area hours earlier saw passengers being spirited away onto wooden boats by people dressed in green fatigues.
The government sent troops to try to cordon off a huge area of the San Lucas range, a mountainous rebel region where the kidnappers are thought to have headed with the passengers and crew.
A spokesman for President Andres Pastrana said Tuesday, however, that a rescue attempt was unlikely. "I don't see that as a possibility," Otto Gutierrez told Caracol radio.
No senior government officials were aboard the plane, whose passengers included an Ecuadorian nun, an Italian lay Catholic worker, an elderly couple in failing health and a three-month-old baby. The U.S. Embassy said it was trying to confirm local media reports an American was on the plane.
Colombia's weak central government has little or no control over vast areas that are dominated and terrorized by an assortment of increasingly brazen armed groups. Security at airports is notoriously lax. Drug trafficking has bred rampant corruption. And the rich and prominent protect themselves with phalanxes of bodyguards.
On Tuesday, fierce fighting was reported in a northwestern region where 43 soldiers were ambushed by guerrillas late Monday. At least 10 soldiers were killed and reinforcements were meeting heavy resistance, the army said.
A country of 40 million, Colombia has the world's highest kidnapping rate and roughly 27,000 murders a year, including some 3,000 political killings. The civil conflict pits leftist guerrillas against right-wing paramilitary groups and government security forces.
More than 2,200 people were kidnapped last year alone, about half of them by ransom-seeking rebels who regularly mount roadblocks on major highways. Such abductions have become so common that many Colombians fly even on short domestic trips. Now it appears even the skies are not safe.