Many tourist vehicles were stuck at both ends of the landslide-affected stretch.
Sikkim was cut off from northern West Bengal's Siliguri on Thursday following landslides in both states triggered by heavy overnight rains.
National Highway connecting Darjeeling district's Siliguri to the Sikkimese capital Gangtok was inundated by the Teesta river at Gailphola around noon on Thursday, leaving hundreds of tourists stranded.
Many tourist vehicles were stuck at both ends of the landslide-affected stretch.
The PWD department said its workers have started constructing a new road by cutting through the mountainous terrain.
Another landslide occurred at Mongpong Anear Sevok, partially stalling traffic movement. There were reports of landslides from Sikkim also.