THE A487 between Bow Street and Tre'r Ddol is currently closed following a collision.
Police are urging motorists to find alternative routes between Aberystwyth and Machynlleth with buses taking a longer route via Ynyslas.
Dyfed-Powys Police said: "Rhydypennau - Treddol.
"The road is currently closed due to due a collision
"Please avoid the area and find alternative routes for your journey."
Lloyds Coaches warned that the closure will cause disruption to its T2 and T28 services, posting on social media: "Due to an accident between Talybont and Bow Street the A487 is currently closed with buses stuck either side of the accident.
"Please bear with us
"Buses will divert via Ynyslas and Borth with longer journey times
"Buses will be unable to serve Talybont or The Wildfowler in Tre'r Ddol
"The 0737 Aberystwyth to Bangor is stuck at the scene and unable to turnaround, this journey is cancelled as a result.
"The 1235 Bangor to Aberystwyth will start from Caernarfon today."