Police say they have broken up the criminal activities of a violent gang known as DLAST HR after a series of raids across south-west Sydney.

Thirteen people were arrested and drugs, weapons and cash seized as dozens of specialist officers swooped on numerous homes in an operation that began early on Monday.

"DLAST HR is a violent, organised gang that has been involved in public-place shootings, vicious assaults, drug dealing and extortion," NSW Police Commissioner Andrew Scipione said.

"We are confident today's arrests will seriously disrupt the business dealings of this particular syndicate."