Sydney has been struck by violent brawls for the second night in a row as calls intensify to address alcohol-related violence in the inner city.

Police said they broke up two brawls on Saturday - one at World Square and one on George Street, near Angel Place, in front of the Ivy nightclub.

There were also numerous other fights and assaults. One man was found unconscious in Sussex Street after a suspected assault and another was stabbed in the head in a separate attack.

Police said when they got to the site of the brawl on George Street they found a large group of people congregating on the footpath and behaving aggressively.

Officers said they issued a number of move-on directions to disperse the crowd; but two men allegedly refused to move on and confronted police and they had to be restrained.

They said they expected criminal infringement notices for offensive behaviour over the matter.

An Ivy spokeswoman said on Sunday morning that "the individuals left Ivy without incident".

"The issues that developed occurred later and off the premises. The police managed this accordingly."

Two men will face court next month after police had to use capsicum spray to break up a fight in World Square about 4.30am.

Police tried to speak to a 22-year-old man when his friend allegedly tried to stop them.

He was charged with assaulting police and resisting arrest and granted conditional bail to appear in the Downing Centre Local Court on February 20.

His friend, also aged 22, was charged with resisting arrest and will appear in the Downing Centre Local Court on February 13.

Police were also called to Redfern Street about 10.30pm after reports that a man had been injured.

The victim had stab wounds to the head and was taken to St Vincent's Hospital for treatment.

Members of the public with more information are urged to contact Crime Stoppers.

Another man had to be hospitalised after he was punched in the face by an unknown man after leaving a hotel on Sussex Street, Haymarket, about 4.35am.

The 21-year-old man was knocked unconscious, fell to the ground striking his head on the footpath.

He was taken to St Vincent's Hospital for treatment of a head wound.

Police said they are investigating the assault, and are looking for a man who has only been described as being of Asian appearance.

In another incident, a 23-year-old man was waiting for a taxi on Wheat Road, Cockle Bay, when another group approached them.

Police were told that, as a taxi pulled up, the group jumped the queue and got into the car and one of the men punched the 23-year-old in the face.

He did not require any medical treatment.

Police are looking for a man described as being of Mediterranean appearance, aged in his 20s and wearing a red chequered shirt.

Another assault left a 20-year-old man with minor injuries, but not requiring hospital treatment.

A 22-year-old man will face Downing Centre Local Court on February 10 over the alleged assault, which police said occurred at a hotel on Liverpool Street about 1am.

Police are also investigating after a fight broke out between a group of men in Hyde Park about 3.40am.

Officers allege that during the incident one of the men was head-butted and was taken to St Vincent's Hospital for treatment of minor facial injuries.

The violence follows two brawls on Friday night, where four men were knocked unconscious during two unrelated fights in Haymarket and Martin Place.

Police said Operation Simmer VI, focusing on Sydney CBD, Darlinghurst and Kings Cross, was conducted in the city over the weekend as part of a summer-long crackdown targeting alcohol-related crime and anti-social behaviour.