The collision occurred in the early hours of Thursday morning when the heavy vehicle allegedly veered into the bus lane. The crash killed four people instantly, and another passenger died later in hospital.
The bus driver, Luis Urueta, said he was preparing to take a curve when he suddenly found himself face-to-face with the truck and swerved to avoid hitting it.
Orlando Gutierrez, one of the passengers, said he felt a strong blow on one side of the bus, before it fell to the side of the road.
The injured passengers were taken to a local hospital. Seven of them were later transported to medical care facilities in Cartagena due to the severity of their injuries.
The tractor-trailor was on its way to Barranquilla from Bogota carrying products for recycling. Government official Ruben Carrillo said an investigation was underway into whether the driver could have fallen into a “so-called micro-sleep” while at the wheel.