Police say the lack of details about two missing trampers intentions in Kahurangi National Park leaves a very large area to search.
Jessica O'Connor and Dion Reynolds, both 23 and from the Tasman area, entered the park on 9 May.
Police say no heat or light sources were spotted by the Royal New Zealand Air Force NH90 helicopter that searched inland from the Anatori River mouth overnight.
Incident controller Senior Constable David Coggers said they had now expanded the search up to the Heaphy area and into Farewell Spit.
Coggers said 27 volunteers were assisting with the search either in the field or at the forward base, with another eight volunteers set to join the search effort tomorrow.
He said no positive new leads were found today.
Coggers said a complicating issue is the fact that the pair didn't leave any information about their plans, or how long they intended to be in the park.
"The issue we have always had from day one is that we have no intentions," said Coggers.
"We have a road, and at the end of that road is a car that has been parked, and from there its a gateway to many many big valley systems and coastal walks. So with no start time, date or intentions we've got to widen our search area to cover all possibilities."
He said there was different reports of when the pair would finish their tramp, and that had not helped with the search urgency.
He said he was hopeful they would be found alive, as the weather had been good, O'Connor had training in the outdoors and they believedthe pair were well prepared.
Reynolds's mother Kath Ludlow said she and her partner were still hopeful for the best outcome.
She said the search and rescue teams and the army had been amazing, working tirelessly night and day to find the missing pair.
Late last night two other teams were winched into the river's headwaters and today will work their way downstream.
Anyone with information should contact Police on 105 and quote event number P042228949.