Dyfed-Powys Police said the incident had taken place in Newtown, near to the Spar shop on Broad Street, at around 1.50am on Sunday.
Police said that one man was taken to hospital as a result of the incident.
A 22-year-old man has been arrested on suspicion of assault and released on bail pending further police enquiries.
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 firstname.lastname@example.org, or by calling 101.
Alternatively, people can contact Crimestoppers anonymously on 0800 555111.