'Can't take chances': cops get broad knife-search power

Police will not need a warrant or suspicion before using the metal-detecting wands on random individuals under the measures, which came into effect on Monday.

The designated zones include shopping precincts, sporting venues and public transport stations.

Senior police can make a declaration allowing officers to scan people for 12 hours in an area where knife- or weapons-related violence has taken place in the past 12 months.

New laws were introduced after incidents including the Bondi Junction shopping centre attack. (Steven Saphore/AAP PHOTOS)

The laws came after a spate of high-profile knife incidents in Sydney, including the Bondi Junction shopping centre attack in April that resulted in six people being stabbed to death.

The changes have been criticised by civil-liberties groups and others for disproportionately impacting vulnerable communities and subjecting people to possible surveillance or harassment. 

But Premier Chris Minns said the laws were life-saving.

"I know that these new laws will be inconvenient for people - but we can't take chances when it comes to public safety," he said.

"To send a strong message to young people in particular, if you're going to go out at night, don't take a knife with you because there's a very good chance you'll be wanded or scanned at a train station."

Police Minister Yasmin Catley said knife crime was happening far too often and the government was committed to stamping it out.

"These new powers give police further capability and resources to quickly detect concealed knives before someone has the chance to use them," she said.

"Police work tirelessly to keep us safe and this reform allows them to continue this important work."

The NSW government also recently doubled penalties for knife possession to a maximum of four years.

The laws align NSW with Queensland, the Northern Territory and Western Australia, all of which have announced or rolled out wanding powers for police.