An earthquake measuring 8.7 on the Richter scale rocked the Indian Ocean off the coast of Indonesia's Sumatra Island on Monday.

The US Geological Survey said it is an aftershock of the quake of magnitude 9.0 that struck the same region in December 2004.

It has also warned of a possible tsunami.

The quake, around 2130 IST, occurred in the same Indonesian region that triggered the Asian tsunami disaster on December 26.

In India, the home ministry has activated the tsunami control room. The Kanyakumari district administration has started evacuating people.

Sri Lanka [Images] and Thailand have also issued tsunami warnings.