The train was travelling from Vigo, Galicia, to Porto in Portugal when the accident happened at around 9.30am local time (7.30am GMT).
Primeiras imaxes do accidente de tren no Porriño. Hai feridos. pic.twitter.com/SKikiiX8pg
At least four people died in the crash in the town of O Porino, while 47 others were left injured.
Local newspaper Diario de Pontevedra reports that the train driver was among those who died in the collision.
The train was carrying 63 passengers, the driver and one other crew member.
Accidente de tren de pasaxeiros agora no Porriño, Pontevedra. Espero que non haxa nada que lamentar. @Renfe pic.twitter.com/UqXrJepWos
O Porrino mayor Eva Garcia de la Torre said the train hit the base of a bridge before derailing, El Pais reports.
Pictures from the scene showed the train’s front carriage flipped onto its side and rammed up against an electricity pylon next to the track.
The derailment occurred on a straight stretch of track close to O Porrino station.
Emergency services dispatched doctors to the scene in helicopters, the regional government said.
The public body which manages Spain’s railway infrastructure, Administrador de Infraestructuras Ferroviarias, has opened an investigation.
The accident prompted five political parties to suspend election campaigning for the day.
News Source SkyNews