NAC chairperson Sonia Gandhi today said the Rohtang tunnel construction was a "happy and historic" occasion for the nation, but asked the Border Roads Organisation (BRO) to ensure that there was no ecological degradation during the drilling.

She also expressed the hope that the BRO would complete the 8.8-km tunnel work within the deadline of 2015, when it would be thrown open for the public to drive through from Manali to Keylong without having to touch the icy heights of Rohtang Pass at an altitude of 3,978 metres.

"A little while ago, I laid the foundation stone for the Rohtang tunnel. It is both a happy and a historic occasion. With this, the dream of former Prime Minister Rajiv Gandhi has become true," Gandhi said at a public meeting here, about 15 km south of the Rohtang tunnel's south portal.

"Expanding roads, constructing tunnels and building bridges are important, but the BRO should ensure that these activities do not damage the ecology of these regions. This will only secure the lives of the future generations in the region. I hope the BRO will keep this in mind while carrying out the construction work," she said.