A once-vital destination during the COVID-19 pandemic is set to be consigned to history, with the last pop-up testing clinics in NSW to close.

"The time has come to close down those temporary PCR testing facilities," Premier Chris Minns told reporters on Tuesday.

The announcement had not filtered through to clinics on Tuesday afternoon, with a sign outside a Merrylands facility reading: "Free COVID testing will remain open in 2023".

A total of 164 COVID-19 PCR test clinics are still operating across NSW, including 52 drive-in only clinics, and 64 walk-in facilities.

"They're temporary facilities. They're not meant to be permanent," the premier said.

"We travelled past one on the way to come to this press conference in Fairfield and it was empty.

"We need to make sure that public money has been protected."

"A lot of money" was currently being spent on maintaining the testing centres, which were largely no longer required as pandemic-related restrictions were wound back, he said.

Health Minister Ryan Park will initiate steps to closing the pop-up clinics in the next 24 hours.