Atop one of the world's most dangerous mountains, former special forces soldier Nirmal Purja MBE was just days in to his world-record attempt to climb all 14 peaks of the Himalayas in seven months when he learned that a fellow climber was missing.

Mr Purja, or 'Nims' as he is known, was descending Mount Annapurna in Nepal on Tuesday when the ex-Special Boat Service soldier was alerted that Dr Chin Wui Kin, 48, had been separated from an accompanying group.

The mountain is the 10th tallest in the world and is considered the globe's most dangerous 8,000-plus metre peak. It was the first of 14 to be tackled by Mr Purja and his team as part of 'Project Possible', an attempt to break the current world record by more than seven years.

Dr Chin, an anesthesiologist and accomplished climber, had been left stranded for 36 hours on his own without an oxygen bottle, food and water after he became separated from a 13-member expedition during his descent from the 26,545 foot summit to base camp four - the first stop on the way down.

It was at camp four, at nearly 25,000 feet, that Mr Purja and his team discovered that Dr Chin was missing. However, rather than set back out up the mountain to find the Malaysian national, Mr Purja was first forced to descend to base camp to retrieve oxygen for the rescue mission as a helicopter was unable to send any up.