Officials said that visitors from all over the country on way to the lake and Nathu La have been put up in shelters provided by the Army at their bases beyond 15 Mile.
The tourists were stuck after boulders fell on the main Jawaharlal Nehru Road, the link between Gangtok and Tsomgo Lake, yesterday.
Lukendra Rasaily, president, Travel Agents Association of Sikkim (TAAS) said the boulders started falling on the road after 2 PM yesterday and at around 4 PM it got totally blocked after another landslide struck above 15 Mile.
Many of the tourists who had reached the spot before the landslide were, however, lucky to make it to Gangtok.Some of the tourists braved it across the slide through other alternative routes to reach Gangtok, but the route was fraught with danger in view of fading light and continuous rains, Rasaily said.
Border Road Organisation officials were working round-the -clock on re-opening the route depending on the weather, the sources said, adding last September's tremor, 6.9 on Richter scale, could have loosened the ground underneath and continuing rains then resulted in the landslide.
The alternative route via Rongli and Rhenock will be used to evacuate the tourists if the main route takes longer to be restored.
Yesterday, was the first day of the week when Nathu la was open to tourists as any traffic upto the Indo-China border remains closed on Mondays and Tuesdays.