Itanagar, Aug 31 (IANS): Four Army helicopters remained on standby to undertake an aerial search once the weather clears to trace Tapi Mra, the first mountaineer from Arunachal Pradesh to conquer Mount Everest, and his associate Niku Dao, who had gone to climb the state's highest peak, defence officials said on Wednesday.

Defence spokesman Lt Col Mahendra Rawat, quoting Deputy Commissioner of East Kameng district, said that the two members of the expedition have been untraceable since August 17 as reported by the remaining six members of the expedition who reached Seppa from their expedition base camp on August 29 evening.

The state government has sought help from Indian Army's Tezpur-headquartered Gajraj Corps in the search and rescue mission.

"Indian Army has already mounted the operation. Two ALH and two Cheetah helicopters have been put on standby, these would be used for aerial reconnaissance of the area with one of the team members onboard once the weather clears," Lt Col Rawat said.

He said that Army's highly trained and motivated special forces and Arunachal Scouts teams are also being employed for the ground search operations in the challenging terrain of the expedition area.

East Kameng district officials said that Mra and Dao were reported missing since they had embarked on scaling Arunachal Pradesh's highest snow-capped peak 'Khyarw Satam' (6,900 metres).

A district official said that special rescue teams are all set for a search operation if any clues on the actual location of missing mountaineers are found and if necessary rescue teams would be airdropped for evacuation.

It takes about a week to trek to the base camp (5,000 metres) of 'Khyarw Satam', which is not only tough terrain, but also needs a trek through dense forests to reach the place.

Mra, 37, had climbed the highest peak of the world on May 21, 2009.

Chief Minister Pema Khandu prayed for the safety of the missing mountaineers and said that the state Sports Department is ready with plans to trace them.