The incident happened on the line near the village of Llanbrynmair in Mid Wales at about 7.30 pm local time.
Dyfed-Powys Police confirmed a man had died and said 15 others had been taken to hospital with injuries that were not believed to be life-threatening or life-changing.
It said all other passengers had been evacuated from both trains.
The British Transport Police said officers were called after reports of "a low-speed train collision involving two trains."
Paramedics, fire and rescue and Dyfed Powys Police were sent to the scene, police said.
AzVision.az
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