Spate of flash floods in the Teesta River have left three people dead and 23 Army personnel missing in Sikkim.
The surging water level over- topped low lying areas and entered the Army establishment at Lanchen valley, Indian media reported.
Floods have devastated several buildings and bridges and a multi-approach rescue operation is underway.
All police stations in the low-lying areas were put on alert, and residents living along the river banks have been asked to evacuate, said The Print.
The small town of Chungthang in North Sikkim is said to be completely cut off from the rest of the region, after flood waters damaged a bridge that connects Mangan and Chungthang, it added.