New South Wales Police have arrested 13 people during morning raids on 20 properties across south-western Sydney.

Dozens of police have taken part in the raids targeting gang-related activity.

Two car dealerships and the office of a real estate agent in Liverpool were among the premises that police raided.

A property on Bellfield Avenue in Rossmore has been searched.

Detectives say those arrested are in the process of being charged by local officers.

Police will hold a press conference this afternoon to announce the details of the raids.