There are 769 long-term missing persons in NSW. Police have approximately 330 unidentified bodies or human remains cases, and just over 100 unidentified bodies or partial human remains are physically on hand with NSW Health.

The police's Missing Persons Registry has reviewed all 769 cases and identified a lack of DNA profiles for a significant number of historical investigations.

The police and NSW Health have developed DNA profiles for all unidentified bodies and human remains on hand.

State Crime Commander Acting Assistant Commissioner Darren Bennett said in a statement that collecting DNA samples is an important part of investigations into missing persons, unidentified bodies and human remains.

"Due to passage of time, there is very limited opportunity for investigators to gather direct DNA for historical long-term missing persons," he said.

"The objective now is to collect familial DNA from the relatives of missing persons across the country to facilitate further inquiries and in the hopes of matching these samples, locate loved ones and provide answers to families."

Biological relatives of historical missing persons will be asked to attend two pop-up centres in Coffs Harbour and Port Macquarie in February to give DNA samples through cheek swabs. The samples will then be uploaded into a database, and searched against another database for unidentified bodies.

Investigators will also interview family members.

Police Minister David Elliott said in a statement that the NSW Police Force is determined to find answers for as many families as possible.

"I would encourage anyone who is looking for answers after the disappearance of a family member to come forward and potentially find closure," Mr Elliott said.

"Every one of the long-term missing people has loved ones who have been seriously impacted by their loss and it is crucial that we do everything in our power to ease their pain."

Australian Associated Press