Siliguri, Sep 19 (IANS): Five teams of the National Disaster Response Force (NDRF) were unable to reach quake-hit Sikkim early Monday as landslides damaged the national highway, snapping the hill state's only road link with the outside world.

The first team of NDRF reached Bagdogra airport in Siliguri in Sikkim's neighbouring state of West Bengal at 2 a.m. Monday, but were unable to proceed as national highway 31 A was damaged by landslides triggered by Sunday's powerful earthquake.

Besides the first team, four more teams of the NDRF comprising 400 rescue personnel have also reached Siliguri but their journey to Sikkim was also halted due to landslides on the highway.

"Five teams have already reached the Bagdogra airport with relief material and medicines. They are waiting for the highway to open so they could move out of Sikkim," said Soumitro Mohan, district magistrate, Darjeeling.

The toll in Sunday's quake, which had its epicentre at the Sikkim-Nepal border and affected northern and eastern India, has risen to six in West Bengal with over 200 injured in the state's northern districts, police said early Monday.

At least 18 people have died in Sikkim.

Around 30 people are believed to have been killed by Sunday's powerful earthquake that measured 6.8 on the Richter scale.