Police searching for missing Swedish hunter Hans Christian Tornmarck have located a sleeping bag and tent believed to belong to him.

Tornmarck, 27, went hunting on May 12 in the Karangarua region, south of Fox Glacier, and has not been seen since. He was due out of the bush three days ago.

Police said in a statement that five search teams had been focusing on the upper reaches of Regina Creek in the Karangarua Valley today. Weather conditions were vastly improved on yesterday.

A helicopter had also conducted an aerial search.

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"Based on inquiries made, searchers have been able to confirm a positive sighting of Mr Tornmarck, which has helped search teams direct their efforts," the statement said.

"Search teams have located a campsite believed to be that of the missing man, including a sleeping bag and tent."

The search was expected to wind down this evening due to tricky terrain and the need to rotate searchers. It was intended to resume tomorrow.

Hans Christian Tornmarck went hunting by himself on May 12. Photo / Police
Hans Christian Tornmarck went hunting by himself on May 12. Photo / Police

Metservice meteorologist Tom Adams said tonight was expected to be the coldest since Tornmarck left on his trip, with temperatures forecast to drop to -5C.

"From May 12 he was looking at a few days of fairly fine weather which is probably why he left then - cold but fine.

"But that ridge only lasted until about the 17th and then a big trough came in from the Tasman which brought quite a lot of rain to the area and strong winds, and that has been followed up by a cold southerly that we're seeing right now."

There would have been significant rain in the two days from the 16th and then on the 18th temperatures started dropping.

Until then overnight temperatures have fluctuated between about 5C and 10C.

The morning of the 18th saw temperatures drop to 4C and last night it went to 1.5C.

"It could easily have been colder in the bush," Adams said.

"With clear skies at night the next few nights are looking particularly cold. It's expected to get to -5C tonight in the area and -2 tomorrow night, 1C Monday night and 2C Tuesday night."

He said the cold weather would likely remain for the rest of the week.

There was some snow visible on satellite imagery on peaks in the area, which was not unusual for this time of year, Adams said.

Tornmarck's family in Sweden have been notified of the search and are being kept up to date on any developments.

Police would still like to hear from anyone who has been in the Karangarua area, south of Fox Glacier, in the past week. Anyone with any information or sightings is asked to contact Greymouth Police on 03 768 1600.