SYDNEY - More than 20 people have been injured and 16 arrested as race-fuelled violence spread through Sydney's beachside suburbs overnight.

But NSW Premier Morris Iemma says police are in control of the situation, after violence that began at Cronulla Beach in Sydney's south flowed over to other communities.

A series of apparent revenge attacks - including two stabbings - occurred overnight following the unrest at Cronulla, where more than 5000 people gathered yesterday.

Drunken mobs within the crowd yelled racist chants and chased down and bashed people of Middle Eastern appearance at the beach in an extended show of violence.

Police and an ambulance crew were also assaulted as racial tensions peaked.

A total of 25 people, including two ambulance officers, were injured, about 40 cars were vandalised and an Australian flag was burned during the mob scenes.

Police said 16 people had been arrested across Sydney and charged with 42 offences.

Mr Iemma today described the behaviour as "stomach turning" and said it would not be tolerated.

"I saw yesterday people trying to hide behind the Australian flag, well they are cowards whose behaviour will not be tolerated," Mr Iemma told Channel Nine.

"That was the most disgraceful, disgusting behaviour that I've ever seen."

Mr Iemma said he planned to bring together community leaders for discussions about how to prevent further violence.

Police had the resources and the equipment to deal with the violent scenes, he said.

Police were forced to use capsicum spray and batons in their battle to subdue the Cronulla rioters, who pelted officers with bottles and stomped on patrol cars.

Later, a 23-year-old man was injured and more than 40 cars smashed with baseball bats in an apparent revenge attack at Maroubra, in Sydney's east.

A group of about 60 men of Middle Eastern appearance and armed with baseball bats smashed the windows of parked cars about 9pm (11pm NZ).

The group then clashed with local group, the Bra Boys, outside the Maroubra Bay Hotel.

A 23-year-old Maroubra man was taken to Prince of Wales hospital after he was stabbed with a sharp implement, believed to be a stick or nail, in the hip.

Later, a second 23-year-old man was stabbed in the back by a group of males, described as being of Middle Eastern appearance, at a golf club at Woolooware, in Sydney's south.

He was taken to hospital in a serious condition.

Riot police were also called to Brighton-le-Sands, in Sydney's south, overnight to control a group of about 200 brawling youths who had reportedly thrown projectiles at police.

Twelve people were arrested at Cronulla. They will appear at Sutherland Local Court at a date to be fixed.

- AAP