The earthquake measuring 6.8 on the Richter Scale, which hit the east and north east (NE) region, was the biggest in 20 years, officials said.
Records of Central Seismological Observatory here showed increasing seismic activity in the region.
A total 34 quakes of light and moderate intensity were felt in the region in 2009. The area witnessed 26 earthquakes each in 2008 and 2007, while it was 23 in 2006, the data showed.
On February 4 this year, a quake of 6.4 magnitude with its epicentre in the Indo-Myanmar border in Manipur shook the region. An earthquake of similar intensity (6.8) had rocked the northeast on August 6, 1988.
On October 11, 2000 a quake of 6.0 intensity was felt in the region, while on September 21, 2009, another measuring 6.2 had claimed six lives in neighbouring Bhutan, where it was epicentred.
The north eastern region had experienced some of world's worst quakes like the Shillong quake and the Assam quake of 1950 both measuring around 8.5.
An earthquake in 1897 in Shillong plateau had left 1,542 people dead.
The Indo-Tibetan Border Police (ITBP) rescued 15 foreign tourists and 150 villagers from various parts of north Sikkim which was badly affected in this evening's earthquake.
The rescued have been moved to the ITBP battalion's headquarter in Mangan, about 20 km from Gangtok, official sources said.
Around 400 ITBP personnel and four medical teams at Pegong are carrying search and rescue operations, while 300 BSF men each from Siliguri and Guwahati along with doctors and para-medical staff have been rushed to affected areas.
Sources said the search and rescue operations are getting hampered because there is no electricity in the area.
The force's also lost two of its buildings. "Two buildings have collapsed though there has been no casualty. The officers mess too has been hit. The road outside the battalion headquarters has cracked," they said.