The Z-Morh or Sonmarg tunnel, stretching 6.4 kilometres (four miles) beneath a treacherous mountain pass cut off by snow for between four to six months a year, is part of a wider infrastructure drive in border zones.

It helps connect Indian Illegally Occupied Jammu and Kashmir with Ladakh, acting as a stepping stone in opening the Srinagar-Leh Highway all year round to allow rapid deployment of military supplies.

“With the opening of the tunnel here, connectivity will significantly improve,” Modi said, wrapped in a jacket from the freezing cold after cutting the ribbon on the $313 million project that has taken a decade to construct.

India and China, the world’s two most populous nations, are intense rivals competing for strategic influence across South Asia, and their 3,500-kilometre (2,200-mile) shared frontier has been a perennial source of tension.

Beijing and New Delhi agreed in October on patrols in disputed areas, shortly before a rare formal meeting – the first in five years – between Chinese President Xi Jinping and Modi.

Another tunnel on the same route, the 13-kilometre (eight-mile) long Zojila tunnel, is more than halfway completed and slated to open in 2026, according to the information ministry.

The Z-Morh tunnel was the site of an attack in October in which gunmen killed seven workers, part of the decades-long insurgency in disputed Kashmir.

Muslim-majority Kashmir has been divided between India and Pakistan since their independence from British rule in 1947, and both claim the Himalayan territory in full.