Seven persons, all said to be tourists, died in Sikkim on Tuesday forenoon when an avalanche hit the principal highway that connects Gangtok with the China border and popular tourist destinations like Nathu-la, Tsomgo (Chhangu) Lake and Baba Mandir.

Among the casualties is a six-year-old girl. The deceased have been identified as Pritam Maity, 38, from Calcutta; Sourav Roy Chowdhury, 28, from Siliguri; Bal Singh, 32, and Rebya Singh, 6, both from Uttar Pradesh; and Muna Shah Shrestra, 29, Shiva Prasad Lamichaney and Ashika Dhakal, all from Nepal. Four of the 13 injured are from Calcutta.

The Indian Army, along with the Border Roads Organisation (BRO) that functions under the defence ministry, launched search and rescue operations and recovered the bodies.

Twenty people who got stuck in the avalanche were rescued.

According to army sources, around 11.10am, the avalanche hit Jawaharlal Nehru Road. “A massive avalanche hit the Gangtok-Nathu-la JLN Road near MS 15. Troops of the Trishakti Corps of the army and teams of the BRO launched a rescue mission,” said an army official.

“Twenty-seven persons were rescued, including six from deep in the valley, and were shifted to nearby medical facilities of the army. However, seven of them succumbed,” said an army source.

Tourists were not allowed to go to Tsomgo Lake and Baba Mandir on Tuesday because of snowfall, and permits were issued till 13th Mile — a spot on the way to the lake — said sources in the Sikkim police.

“However, some tourists went ahead…. The incident occurred between 13th Mile and 17th Mile,” said a source.

An eyewitness said the huge deposit of snow on the road necessitated an excavator to be engaged by the BRO at the site.

“That is why the vehicles had stopped. Many tourists had got down and a section of them had walked upwards along a patch of ice, clicking photos and enjoying themselves. At that time, the avalanche occurred,” he said.

A video clip that emerged later in the day showed a group of tourists enjoying themselves in the snow when the avalanche occurred.

The state disaster management team and the state police also joined in the search and rescue mission. They rescued 350 other tourists and 80 vehicles that got stranded at the spot.

An avalanche, a resident said, is a rare phenomenon in that part of Sikkim.

“On several occasions, and even a few days back, the army and the BRO rescued tourists who got stranded because of sudden snowfall. But an avalanche on JLN Road is something which we have not heard for years,” said Praveen Lama, who runs cabs for tourists in the hill state.

Weather experts said consistent snowfall and sudden temperature rise might have triggered the avalanche. “A huge pack of ice on an unstable area detached from the slope and hurtled downwards. This might have happened because of consistent snowfall or due to a change in temperature,” said an expert.

Sources said that around 5.30pm, another slide occurred at the same site.“The rescue and search operations have been halted for today (Tuesday) because of inclement weather,” said a source.