Emergency services are at the scene after two trains crashed.
Network Rail and Transport for Wales (TfW) said the crash happened between the 18:31 BST service from Shrewsbury to Aberystwyth and the 19:09 service from Macyhnlleth to Shrewsbury, at about 19:30 on Monday.
The crash happened near Llanbrynmair, in Powys, and the line is closed while emergency services work, a joint statement from the operators said.
“Our main priority is the safety of our passengers and colleagues,” it added.
The lines between Machynlleth and Caersws are also blocked, TfW said, and Dyfed-Powys Police has closed the main A470 trunk road in Talerddig advising drivers to avoid the area.
Residents reported a large emergency services presence including road ambulances and an air ambulance.
A coastguard helicopter is also at the scene, as well as firefighters.
British Transport Police is understood to be in charge of the incident.
It said the crash happened at “low-speed”.
“Paramedics, fire and rescue, and Dyfed-Powys Police are all in attendance and the incident is ongoing,” a spokesman added.