Riot squad helps end wild Sydney party

The riot squad, a police helicopter and a dog unit have helped break up a party of 150 people at a vacant house in Sydney's south.

A police officer was admitted to hospital and a teenager has been charged after a clash between partygoers and police at Gymea about 8pm on Friday.

Police say several glass bottles and other projectiles were thrown at officers who were trying to identify the organisers.

They were called to the View Street property following complaints about a party but the crowd dispersed after the riot squad, dog unit and PolAir arrived as back up.

Police allege a 17-year-old youth assaulted a 19-year-old youth at Gymea Railway Station after leaving the party.

A police officer was then knocked to the ground while trying to arrest the teenager and he was taken to St George Hospital with cuts and swelling to the head before he was later discharged.

The 17-year-old was to face a children's court on Saturday charged with assault and resisting arrest.