A man has died after a house party brawl in which baseball bats were used in Sydney's south-west last night.

According to police, the melee began at an Ingleburn home before spilling out on the street, with more people arriving armed in vehicles, triggering a full-scale emergency response at about 9.40pm.

The NSW Police Riot Squad, the Dog Unit, the Rescue Squad as well as Campbelltown police descended on the Chester Road address, with crowds dispersing after police arrived.

Paramedics found a man, whose age is unknown at this stage, with serious injuries. They were unable to revive him and he died at the scene.

The nature of the injuries has not been disclosed.

Police arrested four men, who were being questioned at Campbelltown police station on Saturday morning, and a crime scene has been set up at the property as the Homicide Squad investigates the circumstances of the man's death.

Police have also blocked off Chester Road between Percy Street and Gertrude Ave to examine the crime scene.

Investigators are urging anyone with information about the brawl to contact Crime Stoppers on 1800 333 000 or crimestoppers.com.au.