The NSW Police Force launched the pilot program on the Mid-North Coast to gather DNA samples from biological relatives of missing persons.

The program aims to assist detectives with ongoing historic missing persons investigations.

Relatives have provided DNA samples at pop-up collection centres at Port Macquarie and Coffs Harbour.

Samples will be used for the purposes of connecting familial DNA to unidentified bodies and human remains in a bid to identify the remains.

Missing Persons Registry manager Detective Inspector Glen Browne said the response from families to the familial DNA collection pilot program had been extraordinary.

"It has been more successful than I could have imagined," he said.

"The families have struggled for so long to get answers and a number of them have come along and have shed tears simply because they have held onto these things for so long and struggled without knowing what happened to their loved one."

NSW has more than 750 long-term missing people and about 330 unidentified bodies or human remains cases.

Advances in science have led to the familial DNA linking capability.

Direct DNA matching is often not possible in long-term missing persons cases.

More familial DNA collection centres at other regional NSW locations will be announced shortly.