New Delhi: A string of high intensity earthquakes off Indonesia on Wednesday led to tremors in various parts of India and triggered fears of tsunami with government issuing warnings which were withdrawn later.

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A massive 8.5 magnitude undersea earthquake, with the epicentre at over 400 km off the northern Sumatra coast, struck at 14:08 IST sending tremors as far as Guwahati and Bangalore and reviving fears of the tsunami of December 26, 2004 which killed thousands of people in India.

Within eight minutes, the Indian Tsunami Early Warning System (ITEWS) issued alert for Nicobar islands which prompted evacuation of people from India's southernmost islands. It also alerted the coastal regions of Tamil Nadu, Andhra Pradesh and Andaman islands for a possible tsunami.

The first quake in Indonesia was followed by at least seven others, including one of 8.2 magnitude on Richter scale. As panic struck the coastal regions, the central and state governments immediately initiated operations to meet any exigency. Two IAF planes were kept for rushing teams of National Disaster Response Force (NDRF) to any affected area.

However, warnings were withdrawn after nearly three hours as there was no sign of the killer waves as predicted by the ITEWS.

"The quake led to a lateral shift and there was not much of vertical movement," Shailesh Nayak, Secretary, Ministry of Earth Sciences said.

Cabinet Secretary Ajit Seth said there was no need for panic and the government was fully prepared. Seth said that he had spoken to Chief Secretaries of coastal states as also the administrator of the Andaman and Nicobar islands. He said warnings were issued and people were evacuated in some vulnerable areas.

Campbell Bay in Nicobar Islands saw a couple of mini tsunamis as high as 45 cm, while Chennai, Ennore and Vishakhapattanam saw sea level rise by 10 cm, nine cm and eight cm respectively.

Operations at Chennai Port were suspended, Metro operations in Kolkata were briefly shut down, fishermen in coastal states were asked to return to land and people in the Little Andamans, southern group of islands including the Great Nicobar and Campbell Bay, were evacuated. The southern islands were the closest to the epicentre of the quake.

Six teams each of National Disaster Response Force were kept in readiness at Chennai and Hindon airport on the outskirts of Delhi, the Cabinet Secretary said.

"After the last tsunami we have put a robust system in place and it worked well," he said, adding it was a good drill to test the response systems.

Chennai's iconic Marina beach was evacuated but people stayed on its fringes to watch the raging sea. Operations at Madras Atomic

Power Station (MAPS) in Kalpakkam near Chennai continued to function normally though there was a move to halt operations following the Tsunami warning.

People rushed out of houses and high rise office buildings in panic in cities like Chennai, Bangalore, Thiruvananthapuram, Kochi, Kolkata, Bhubaneswar and Guwahati where tremors were felt.

The ITEWS issues alerts automatically within seven minutes of an earthquake of greater than 6.5 magnitude hits the Indian Ocean. Further bulletins are issued after expert analyses the data gathered from various sources.

As officials were preparing to withdraw the tsunami warnings issued after the first quake, an aftershock of 8.2 magnitude hit the same region prompting officials to mount vigil as computer models projected 1.7 meter high waves lashing Indira Point on the Great Nicobar Island.

However, this quake also did not generate the tsunami which was apprehended. Meulaboh in Indonesia recorded a 20 cm rise in sea level as a result of the quake, which could be seen as a mere ripple in the water.

Scientists said tsunami waves travel at high speed of 500-700 km per hour and would have taken less than half an hour to reach Nicobar. The waves, if triggered, would have taken two to three hours to hit the southern coast of India which was over 1800 km away from the epicentre.

Nuclear engineers at the Kudankulam nuclear power plant continued with their work towards commissioning of the project which was delayed eight-month long protests over safety concerns.

"We received the alert from Indian National Centre for Ocean Information Services in Hyderabad and we are generally on alert. But our work is continuing," M Kasinath Balaji, Site Director, Kudankulam Nuclear Power Plant said. He said the walls of KNPP are 7.5 m high and the plant itself is situated on a raised platform.

In Kerala, people felt the tremors in Thiruvananthapuram and Kochi. In Karnataka, tremors were felt in Kodigehalli, Yelahanka, Mathikere, Palace Road, Infantry Road and R T Nagar.