The family of a tramper who has been missing in Mt Aspiring National Park since Friday are on their way to New Zealand to assist with the search.
UK woman Stephanie Simpson, 32, failed to turn up for work on Monday after telling friends she was tramping in the area at the weekend.
Speaking to UK station Sky News, brother-in-law Sam Hazelton said her family last heard from her on Thursday.
"She is such a fun-loving, kind, determined and adventurous woman, we are asking anyone who might know anything to get in touch with police.
"We are all so worried and desperate for information."
Simpson's parents are on the way to New Zealand to help look for their daughter, Sky News reports. Drones and thermal imaging will be deployed on Wednesday as the search for her continues.
In a statement, police said search teams remained in the park overnight navigating a large search area - much of it difficult terrain.
Resources are being boosted on Wednesday morning with up to 40 people expected to be involved in the search.
Described as being fit and experienced, Simpson had been tramping regularly while working in Wanaka as a gardener.
"The search continues to focus on the area from Fantail Falls to Mt Brewster, the Brewster Hut and Mt Armstrong track, and also Makarora Valley," police said.
"Anyone with information should call 105 and quote file 200211/4896."