Trampers are being urged not to rely on cellphones after a couple were rescued from a snowy ridge in the Nelson Lakes National Park.
The couple spent hours stuck in the cold on Mount Robert ridge on Saturday, Sergeant Steve Savage of the Nelson police said.
Police were alerted about 8.30pm that the couple were unable to reach the Angelus Hut.
They were trapped on the ridge in the darkness, just 700 metres from the hut, but were unable to continue because their gear was insufficient for the alpine environment.
The couple were fortunate to be able to find an area with cellphone coverage and police were able to work out their location, Sergeant Savage said in a statement.
They were located at around midnight by the Nelson Marlborough Rescue Helicopter.
Both were feeling the cold, but otherwise in good health.
"This is a route in which conditions can change from being hot and sunny to strong winds, snow or rain with subzero temperatures in the matter of one hour," Sergeant Savage said.
"There have been two fatalities in this area over recent years as well as numerous lives saved.
"The couple were fortunate, as they had insufficient gear to spend the night out in the snow."
He said police encourage trampers to carry a personal locator beacon, and never rely solely on cellphones for communication.
The beacons allow rescuers to identify a person's location instantly and they work almost anywhere.
They can be bought for around $500 and will last 10 years.
Trampers and other users of the outdoors should also carry torches, emergency shelter and suitable clothing, police say.