Two men charged over separate alleged assault at Sydney CBD fast food restaurants

Police have appealed for witnesses to a brawl at a Sydney CBD fast food restaurant where a 24-year-old man was stabbed in the lower torso.

A man has been charged with having a knife in public, but police are still trying to determine who was responsible for the stabbing.

Detectives are still waiting to interview several people involved in the incident and view CCTV footage.

Emergency services were called to KFC on George Street at 12.20am on Sunday following reports of a fight between two groups.

The wounded man was taken to St Vincent's Hospital in a stable condition and will undergo surgery on Sunday.

Elsewhere in the CBD a man has been charged after he allegedly punched his partner several times at a different fast food restaurant.

The 22-year-old was arrested around 1.45am at a Hungry Jacks on Pitt Street and later charged with assault. He'll appear in court in late December.

The 21-year-old woman has been treated in hospital for extensive bruising.