South Wales Police were called shortly before 3pm to reports of an assault at an address on City Road.
The force said five people went to hospital after suffering “superficial injuries”.
Officers have urged anyone with information relating to the incident to come forward.
Ambulance and fire crews were also deployed to the busy high road this afternoon.
South Wales Fire and Rescue Service confirmed they were “assisting” and said it is a “police matter”.
A South Wales Police spokesman said: “At around 2.44pm today emergency services attended an address on City Road, Cardiff, after reports of an assault.
“There is quite a large police presence in the area and members of the public are advised to stay away from the area while it is being dealt with.
“Five people attended hospital with superficial injuries.
“Officers are appealing for anyone with mobile phone or dash-cam footage of the incident or the aftermath to please contact us quoting ref 2100312749.”
This is a developing news story, more to follow