Separate teams of officers and jawans from the Eastern Command battled throughout much of Wednesday trying to locate 22 army personnel, who went missing from its base camp in Lachen valley following the sudden cloudburst on Lhonak Lake.

The number includes two Border Roads Organisation (BRO) workers from spots close to the base camp.

"Release of water from the Chungthang dam led to a sudden increase in water level up to 15-20 feet high downstream. This has led to army vehicles parked at Bardang near Singtam getting affected. Twenty-three personnel have been reported missing and 41 vehicles are reported submerged under the slush," the army said in a statement on Wednesday. Later in the day, Trishakti Corps rescued one soldier.

A stone crusher plant of the BRO under the defence ministry was washed away at Toong in the north, along with old police barracks, sources said.

Officers said the BRO plays a crucial role in building and maintaining roads stretching over 900km in the eastern and northern parts of Sikkim. The area remains under intense scrutiny of the army because of the Nathu La pass that stands between China's Yadong County in Tibet and the northern tip of Sikkim.

In January 2021, Nathu La was at the centre of attention when Chinese and Indian troops reportedly clashed in a disputed border area when a Chinese patrol allegedly tried to enter the Indian territory and was pushed back.

"Sikkim's location in the geo-political space and its borders with China makes it a very crucial area for surveillance by the Indian army. Realising this the defence ministry had re-raised BRO's famed 'Project Swastik' in 2008 to build infrastructure along the border," said a senior army officer.

"The BRO continues to have its formidable presence across parts of Nathu La, Dzuluk, Changu, Lachen, Lachung, Chandmari, Rongli and Melli."

Sikkim's border possibly remains the only area for the Indian army to launch an offensive in response to any Chinese incursion, a section of military experts said.

Sikkim's border is also the only stretch of the Himalayan frontier where Indian troops have a terrain and tactical advantage. They have higher ground, and the Chinese positions there are squeezed between India and Bhutan, they said.

"Bridges getting washed away and roads getting severely damaged in floods will be a setback for both the civil and the army establishments in Sikkim," the officer said.

Senior officers said they were yet to take stock of the damage since it can only be done once the waters recede. Tracing the missing army personnel was of utmost importance now, they said.

"The waters are difficult to negotiate and the darkness of the night is making rescue and relief operations extremely challenging," the officer said.

Additional reporting by Avijit Sinha in Siliguri