Dyfed-Powys Police is appealing for witnesses who may have information about a single-vehicle road traffic collision on the A470.
The collision took place on the Rhayader to Llangurig stretch, approximately one mile north of Rhayader at around 1:30am on Tuesday, August 6.
The collision involved a green Volvo estate.
One adult male was taken to hospital with serious injuries where he remains in a critical condition.
One man, age 23 has been arrested on suspicion of driving whilst over the prescribed limit and causing serious injury by dangerous driving.
Investigating officers would particularly like to speak to any motorists who may have been travelling along the A470 - Rhayader to Llangurig at that time who have a dash cam in their vehicles.
Quote Reference: 26 of 6th August.
Police can be contacted either online at https://bit.ly/DPPContactOnline, via email at [email protected], via direct message on social media or by calling 101.