Seven tourists were killed as a massive avalanche hit Sikkim's Nathu La area on Tuesday morning, burying their vehicles under the snow, officials said.

The avalanche hit the arterial Jawaharlal Nehru Marg, which connects Gangtok to Nathu La at the China border, around 11.30 am, trapping five-six vehicles with around 30 people under the snow, the Army said in a statement.

Till 4 pm, seven bodies were brought out of the snow and 23 people were rescued alive, including six tourists from a deep valley, a state government official said, quoting reports from the Army.

Among those dead are a woman and a child, he said.

Search operations in the area are underway by the Army, state disaster management teams and police to find if any other person is trapped, officials said.

Those injured were admitted to different hospitals in Gangtok, around 55 km away, they said.

Union Home Minister Amit Shah said the Centre was closely monitoring the situation, and the teams of the NDRF will reach the area -- between Milestones 13 and 17 -- soon.

"My sincerest condolences to the families of those who have lost their lives in the tragic avalanche in Sikkim. We are closely monitoring the situation and the teams of NDRF will reach the affected area soon. I pray for the speedy recovery of those injured," he tweeted.

Nathu La, situated at 14,450 feet above the sea level, is one of the three open trading border posts between India and China. It is a major tourist destination because of its scenic beauty.

The tourists were not permitted to travel beyond Milestone 13 due to inclement weather, but they forced the tour operators and the drivers to take them to the area where the incident happened, a police officer said.

The road has been opened for traffic by the Border Roads Organisation (BRO) as the snow was cleared, the Army said.

Some 350 people in 80 vehicles, stranded on the road because of the snow, were being brought back to Gangtok, officials said.

Chief Minister Prem Singh Tamang condoled the deaths, and said that he was praying for the speedy recovery of those injured.

"My heart goes out to the bereaved family and friends in this hour of grief and I pray that the departed souls rest in eternal peace," Tamang said.

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