At least 13 people were injured in the southwestern Colombian province of Valle del Cauca when a fireworks-filled suitcase exploded on a bus which then caught fire, government officials said.

A local official in Candelaria, the town where Friday's blast occurred, told reporters that a passenger apparently put his suitcase near the vehicle's motor, which caused the fireworks to heat up and explode.

Eberto Riveros said that for now it is "pretty difficult" to establish which of the passengers owned the explosive material, but added that authorities are investigating the matter.

Most of the injured were hospitalized, including four who are in fairly serious condition and were later transferred to another medical center.

Though exactly how many passengers were on the bus remains unknown, estimates indicate there were at least 25. EFE