Six males have been charged after a violent brawl broke out in the Melbourne CBD in the early hours of Saturday morning.

Two groups clashed at the corner of Flinders and Swanston street about 3.30am, near the steps of St Paul's Cathedral.

Five men, aged 26 to 31, were injured, with four of them requiring treatment in hospital. The patients were from Mt Evelyn, Ferntree Gully and Werribee.

Police are investigating the circumstances that caused the fight to break out.