Dyfed-Powys Police said that the A458 between Middletown and Welshpool was closed due to a collision involving three vehicles at about 10am on Wednesday.
Four people received injuries but did not require transporting to hospital and were discharged at the scene.
Police advised people to avoid the area if possible and find an alternative route while emergency services dealt with the crash. The road reopened at about 12.30pm.
The Welsh Ambulance Service has been asked to comment.
Anyone with information that could help officers with their investigation is asked to report it to Dyfed-Powys Police, either online at bit.ly/DPPContactOnline, by emailing email@example.com, or by calling 101.