A 7.5-magnitude earthquake struck under the Indian Ocean on Sunday, triggering a tsunami watch for nearby islands and causing tremors reportedly felt along India's eastern seaboard.
The quake hit at 1:26 am local time (1926 GMT) at a depth of 35 kilometres (22 miles) with the epicentre around 160 kilometres west of India's Nicobar Islands.
The Pacific Tsunami Warning Center, based in Hawaii, initially issued a warning for the entire Indian Ocean region. This was downgraded to a warning for India only, when the magnitude of the quake was revised to 7.5 from 7.7, and later the centre cancelled the alert altogether.
India's ocean information centre issued a "tsunami watch" for 10-15 islands, but said it was expecting only a mild surge in sea levels of about 50 centimetres (20 inches).
"This is nothing alarming, but just a watch," Sriniwas Kumar, a spokesman from the state-run Indian National Centre for Ocean Information Services told AFP by telephone from the agency's headquarters in Hyderabad.
The tremors were felt more than 1,000 kilometres from the epicentre on mainland India, where many were shaken awake in the dead of night, causing some to flee their homes in panic, the Press Trust of India reported.
Moderate tremors were felt in the southeastern coastal city of Chennai, but there were no reports of casualties or damage to property, according to police.
The US Geological Survey initially gave the magnitude of the quake as 7.7 before revising it down to 7.5.
Indian Ocean islands were badly hit by the 2004 Asian tsunami which was triggered by an earthquake off the Indonesian island of Sumatra and sent giant waves crashing across the region.
The 2004 tsunami killed more than 220,000 people, most of them in the northern Indonesian province of Aceh. Thousands of people were also killed in Sri Lanka, Myanmar, Thailand and India.
The Andaman and Nicobar Islands are some of India's most easterly territories and more than 350,000 people live on the 572 islands flanked by the Andaman Sea and the Bay of Bengal.
The Andaman Sea area witnesses frequent earthquakes caused by the meeting of the Indian tectonic plate with the Burmese microplate along an area known as the Andaman trench.