The epicentre was plotted in Mongar in Bhutan. Mongar, about 500 km from Thimpu, is located along the India-Bhutan border, 125 km northwest of Guwahati.

The tremor caused cracks to develop in apartments and concrete structures in Assam's main city of Guwahati.

'At least five to six apartments in Guwahati developed visible cracks, while two buildings showed signs of slanting due to the impact of the quake,' an Assam government official said.

This is the fifth earthquake to have rocked India's northeast region since Aug 11, Monday's tremor being the strongest.

'The top floor where we stay was literally rocking, swaying sideways with people forced to run out of their homes. The tremor lasted for about 20 to 25 seconds at least,' said Arun Hazarika, a resident of Guwahati staying in a five-storey apartment.

The seven northeastern states - Assam, Meghalaya, Mizoram, Tripura, Nagaland, Arunachal Pradesh and Manipur - are considered by seismologists as the sixth major earthquake prone belt in the world.

The region experienced one of the worst earthquakes, measuring 8.7 on the Richter Scale, in 1897 that claimed the lives of over 1,600 people.