Flash floods and landslides in the annual monsoon rains have killed at least 30 people in India's northeast states in the past week.

The landslide that killed the soldiers took place on Sunday evening in the mountainous state of Sikkim, which shares a border with Nepal and China, and hosts a large military presence.

The army said in a statement that the "massive landslide, triggered by heavy rains, struck an army camp" around dusk on Sunday.

The army posted pictures on social media showing a swath of earth that had semi-submerged a building, and left a giant mud gash on a hillside.

Flash floods are common during the monsoon season, which usually begins in June and eases by the end of September.

South Asia is getting hotter and in recent years has seen shifting weather patterns, but scientists are unclear on how exactly a warming planet is affecting monsoons.