Anyone who may have seen or spoken to missing British tramper Stephanie Simpson in the Makarora area over the weekend is urged to contact police.
The 32-year-old was trekking in Mt Aspiring National park over the weekend and failed to return to her landscaping job on Sunday - sparking concerns for her welfare.
Friends of Simpson have not heard from her since Friday.
A helicopter crew were searching for her yesterday evening, police said in a statement this morning.
And the Fox Glacier Alpine cliff rescue team, a search dog and handler, and Wanaka LandSAR volunteers would continue their search shortly.
"The search area encompasses Fantail Falls to Mt Brewster, the Brewster Hut and Mt Armstrong track, and also Makarora Valley," the statement said.
"If anyone was on the track over the weekend who stayed in the Cameron Flat area on Friday and may have spoken to Stephanie, or anyone who may have seen her on the track from Fantail Falls to Mt Armstrong, or in Makarora Valley, please let Police know on 105."
Police said Simpson was reported missing at 8.45am on Monday. It was unclear if Simpson was tramping alone.
A close friend told the Herald it would have just been "another weekend away tramping" for Simpson.
"She's strong, she's fit, she's capable. She's worked in the outdoors, she knows what she's up to."
She said Simpson arrived from Australia last year alone and has been living in Wanaka since July, working in landscaping.
The friend, who didn't want to be named, described the Brit as "outdoorsy, super friendly and super bubbly", and said she would explore the area as much as possible.
"She's a really beautiful, kind-hearted person. She can make friends in an instant, she's awesome. She's just here to tramp and see the country."
The friend hoped Simpson would turn up soon.
"It wouldn't surprise me if she did just rock up tonight and there's been a little something that's happened and she just needed to take an extra day," she said.
Her disappearance comes after heavy rain battered areas of Southland and Otago last week with rising rivers inundating low-lying homes, businesses and farms.
A state of emergency was declared in flooded Southland, where roads were closed and a steady downpour left homes and farms sodden.
The swollen rivers may have also been responsible for the deaths of two trampers who got into trouble while heading into the Mt Aspiring National Park.
Senior Sergeant Miriam Reddington said their bodies were found in the Makarora River, near the start of the Blue-Young link walking track and just upstream of the confluence of the Young River.
''All our inquiries indicate they were going for a hike.''
One body was recovered on Friday afternoon by the Wanaka Search and Rescue river rescue team, and the second on Saturday.
Reddington said police were trying to establish when the trampers had left.
The deaths were not considered suspicious, and police were not looking for anyone else in connection with the incident, she said.
''We think they have just come unstuck.''
Reddington said police were working with the Department of Conservation to make sure it was safe for trampers to continue using the area.
Central Otago District operations manager Mike Tubbs said the Makarora River fluctuated ''wildly'' as a result of rainfall and snowmelt and the nearest river level monitoring site showed the Wilkin River, which runs into the Makarora, went from 300cumecs (cubic metres per second) to 900cumecs and back to under 100cumecs in the space of four days last week."
The steep walk to Brewster Hut can take up to four hours one-way and is recommended for experienced trampers only.
Trampers cross the Haast River and are advised to exercise caution after heavy rainfall.
MetService meteorologist Tuporo Marsters said the heavy rain that overwhelmed Southland would have begun to recede by the weekend and it was unlikely the Haast River would have still been in flood.