The BBC reported that the earthquake triggered a tsunami warning across the Indian Ocean region.
In India, a tsunami warning has been issued in the Andaman and Nicobar islands only, as of now. TV reports say tremors were felt for at least 12 seconds in the islands.
Tremors were also felt in two phases in Kolkata, lasting a few seconds each. Tremors were also felt in Chennai, Bangalore, Thiruvananthapuram, Kochi, Patna.
The US Geological Survey said the quake’s epicentre was at a depth of 33km, at a location about 495km from Banda Aceh province on the island of Sumatra.
A tsunami watch was issued across 28 countries including India, Pakistan and even UK.
According to agency reports, people on Twitter said tremors were felt in Singapore, Thailand, Malaysia and India.
A massive 9.1-magnitude quake off Indonesia on Dec. 26, 2004, had triggered a tsunami in the Indian Ocean that had killed 230,000 people.
US monitors issued an Indian Ocean-wide tsunami watch following a massive earthquake off the coast of Sumatra.
The tsunami warning center said it had not yet ascertained whether a tidal wave had been generated but that one was likely given the strength of the temblor, and advised local authorities to take "appropriate action."