Although hopes of finding the 31-year-old Macarthur woman alive are fading, police insist the case is still being treated as a search for a missing person. There may yet be a chance that the woman will be located.

The officer in charge of the search, Senior Constable Reg Dwyer, said the search area had narrowed on Friday after police received information from the woman's family.

He said it was possible the woman had strayed from marked tracks after following an out-of-date guidebook.

''We have obtained a little bit more information as to where she might have been from the family, they located the information at home,'' he said.

''We also have obtained that information from rangers about an advertised track, an old track, that wasn't used anymore in a guide book, not produced by rangers, that she had.

''Yesterday [Thursday] we knew she had a guidebook, but we didn't know which one. There are a number of different guide books for the area and this one mentions a couple of different walks that are certainly not walks any more.''

The search intensified yesterday when about 40 State Emergency Service personnel joined 30 police and 10 park rangers.

The searchers were aided by the Snowy Hydro Southcare helicopter, which is equipped with thermal imaging equipment, and a Squirrel helicopter that arrived from Jindabyne.

Senior Constable Dwyer said police had commenced line searches 20 people walking abreast, starting from the track and into the dense scrub after Thursday's preliminary searches revealed nothing.

Police still believed it was possible the woman could survive two to three nights.''She didn't have a great deal of food, she had some snacks, some sandwiches, a couple of drink bottles with her, pants and long-sleeved tops, we believe she had some wet-weather clothing,'' he said.

''She's got enough that if she's ... she could survive two to three nights, so we are still hopeful that we can locate her.''

''There is plenty of water around, running through the creeks, but as far as food supply goes, its obviously very limited. The longer she is out here, the less chance she has.''

The search would continue into next week if necessary and was scheduled to begin again at 6am today.

The missing woman set off at about 8am on Wednesday to hike the 9km round trip of the Nursery Creek walking trail.

Police said the woman's family had visited the police camp yesterday, but said they still did not want to issue her name to the public.