It was around 07.50, in the middle of the morning rush hour, that one train drove into the other from behind, writes Spanish newspaper El Pais.
Around 18 ambulances were sent to the scene, but no one was reported to be seriously injured - as the trains collided at relatively low speed.
- We were waiting for the train when we heard a bang.
Many people fell because the train was full, Pol Viñas from the Spanish train company Ser Catalunya told the newspaper El Pais.
The two trains collided at Montcada in Reixac just north of Barcelona.