Thirty-one children were burned to death when their bus caught fire and exploded in northern Colombia on Sunday, the Red Cross said.
Another 25 people - including one adult - were injured and seriously burned in the blaze at the town of Fundacion, in the department of Magdalena, Cesar Uruena with the Colombian Red Cross told AFP.
"The injured have second and third-degree burns, and many are still in a critical condition" in hospitals in the area and in the city of Santa Marta, Uruena said.
The children aboard the bus were between the ages of one and eight and were returning home after a religious service, Fundacion Mayor Luz Stella Duran told reporters.
Magdalena police told AFP that the bus exploded around noon, and that the fire was so intense they had problems determining the number of casualties.
Stella Duran said that - according to survivors - the bus driver had been handling a container with gasoline aboard the vehicle. Police initially blamed the fire on a mechanical problem.
The driver has vanished, and angry locals went to his home and threw rocks at his windows, the mayor said.
Colombian President Juan Manuel Santos traveled to Fundacion after a final re-election campaign rally Sunday in Bogota ahead of the May 25 presidential vote.
"The entire country is in mourning for the death of these children," Santos said upon arriving in Fundacion, accompanied by his wife.
Santos said that the government would pay for all hospital and funeral expenses relating to the accident.
The bus, which was being used by an evangelical church group, caught fire one block away from the church where the children had earlier attended services.
The Red Cross said it was sending four psychologists and two volunteer specialists in psychosocial aid to help the wounded and the relatives of those killed.