At least 31 children and one adult were killed, and another 18 people critically injured, after a bus caught fire while returning from a church event in northern Colombia on Sunday, media reports said, citing an emergency response coordinator.

The regional police chief, Col. Adan Leon, reportedly said that 18 people, including some adults, had been found alive at the scene of the tragedy in Fundacion, about 465 miles north of Bogota, and were being treated at a nearby hospital, while the dead were being identified with dental records in Barranquilla, the nearest city to Fundacion town where the accident happened. Leon reportedly said that most of the estimated 50 people on the bus were younger than 14. Officials told media that the bus was allowed to carry only 38 passengers.

"There was a canister of gasoline inside the vehicle. The fire spread very fast," Major Eduardo Velez, coordinator of Magdalena province's emergency response corps, told Reuters.

Velez reportedly said that the fire may have started after the driver attempted to start the bus, which had broken down, by pouring fuel into the engine, but added that specific details about the cause of the fire could only be determined after investigation. The driver, who reportedly escaped unharmed, was being questioned by police.

According to CNN, one witness told Caracol TV, a Colombian private national TV network, that the driver had asked children to put gasoline into the vehicle's tank. 

Cesar Uruena, who works for the Colombian Red Cross, told Agence France-Presse: “The injured have second- and third-degree burns, and many are still in a critical condition.”

Colombia’s President Juan Manuel Santos, who was traveling to Fundación, reportedly said Sunday: “The entire country is in mourning for the death of these children.” He also added that authorities would cover funeral and medical expenses that are currently being paid by the victims' families.