SAR Sergeant Mike Fitzsimons said a 19-year-old German woman rang a Department of Conservation ranger about 5.50pm saying she had lost her way.

A search began, using a helicopter crew with night-vision goggles.

Worsening weather meant the helicopter could not get to where searchers believed the woman was, and a three-man team set off on foot.

The tourist had intended to do a multi-day tramp in Nelson Lakes National Park, leaving from the Spear Grass Hut. Fitzsimons said she was believed to be on Robert Ridge, near Nelson Lakes.

"Weather conditions aren't good. She's a lone tramper who doesn't have sufficient experience and obviously made a few bad judgment calls which we are now having to sort out," he said.