Experienced climbers Aleš Holc and Peter Mežnar were members of the expedition Shaksgam 2014, which set out in mid-June to conquer the lesser known Himalayan peaks Durbin Kangri I (6,824 m), Durbin Kangri II (6,898 m), Barnag Kangri (6,821 m) and Kaimuk Kangri (6,952 m).

The Mountaineering Association said they started their climb on 5 July but then failed to report to the agreed meeting place. It hopes they were prevented from returning by the seasonally swelling rivers.

Other members of the mission have checked the area but they could not cross a river that the pair were expected to cross to get back.

A search and rescue mission was launched but there have been problems securing helicopter transportation given the treacherous and remote terrain.

"The latest information suggests helicopter rescue has been approved and a chopper is on its way to the area," the association said.

The rescue mission is being conducted in conjunction with the Foreign Ministry and the Slovenian Embassy in Beijing.