A MASSIVE series of police raids in Sydney has nabbed 13 alleged criminals involved in an Assyrian gang.

More than 20 raids were completed across Sydney's south-western suburbs, targeting members of the gang, understood to be known as The Assyrian Kings.

The raids resulted in the seizure of replica guns, drugs, cash, jet skis, a boat and a car, and police investigations are still under way.

Assistant Commissioner Frank Mennelli told reporters those involved with the gang were allegedly behind recent public place shootings and murders in Sydney.

He said some information had related to marijuana and a "criminal group that have made thousands upon thousands of dollars" through illegal activity.

It is understood the police investigation had been under way for 18 months, with more investigations to come.