The Centre on late Monday night issued a fresh tsunami alert asking authorities in the coastal states and Andaman and Nicobar Islands to keep a 'close watch'.
The alerts followed a massive quake of magnitude 8.2 off the coast of Sumatra at 2138 IST. The US Geological Survey said the quake measured 8.7.
"Since the earthquake is of an intensity greater than 8.0 on the Richter scale, it is advisable to keep a close watch, particularly in the absence of sea-level gauges in the Indian Ocean," Disaster Management Director S K Swami said in a fax message.
The message was sent to chief secretaries of Orissa, Andhra Pradesh, Tamil Nadu, Pondicherry, Kerala, Andaman and Nicobar Islands, Karnataka and Lakshadweep Islands.
The message, sent out at 0030 hours IST, said: "Tsunamis have a history of taking longer time than expected.
"This is to reiterate that tsunami alert should continue till stand down orders are issued by this ministry."
It further said, "There is no need to panic."
It also asked the relief commissioners of the coastal states and the Andaman Islands to be alert.
The home ministry control room would continue to maintain a vigil throughout the night.