The A470 at Storey Arms is closed following a vehicle fire earlier this morning.
The road is closed in both directions between the Defynnog turn off (A4215) and the Hirwaun turn off (A4059).
Police have asked motorists to find an alternative route.
Stagecoach has said that the T4 has delays in both directions and will be diverted via the Heads of the Valleys and Abergavenny, both to and from Brecon. Due to the incident, they are unable to serve Pen y Fan.
A spokesperson for the police said: “Dyfed-Powys Police attended a report of a bus on fire on the A470 between Storey Arms and Brecon at around 1am on September 29.
“All passengers were accounted for and no injuries were reported.
“The road was closed to ensure the safety of the public and to recover the vehicle. The road closure was managed by the council from around 8:30am.”