The US Geological Survey said, "The quake, initially reported as a magnitude 7.7, struck at 01:55 am. It was shallow, at a depth of 20.6 miles (33 km), and was centered 160 miles (260 km) north of Port Blair."
The US National Oceanic and Atmospheric Administration's Pacific Tsunami Warning Center issued a tsunami watch for the region.
Tsunami center said, "Earthquakes of this size have the potential to generate a destructive local tsunami and sometimes a destructive regional tsunami along coasts located usually no more than a 1,000 kilometers (about 600 miles) from the earthquake epicenter."
However, an official at the Indian National Centre for Ocean Information Services said a tsunami warning was not issued by his department.
"We have not issued a tsunami alert and are monitoring the water level changes in the region at the moment," Ajay Kumar told news agency.
On Dec, 2004, about 230,000 people were killed in a dozen countries around the Indian Ocean when a magnitude 9.0 earthquake triggered a tsunami.