At least 20 persons were killed and over 100 injured after a powerful earthquake hit the Andaman and Nicobar Islands on Sunday morning. The quake was followed by tidal waves.

"There is a possibility of the figure going up. Rescue operations are on," Inspector General of Police S B Deol told PTI.

The Andaman and Nicobar Islands, he said, were jolted by the earthquake between 6:30 and 6:35 am. Tidal waves followed the tremor.

Deol said the possibility of the casualty figure going up existed as a large number of people, mainly fishermen, were missing. They had gone out in the sea, as there was no prior warning.

The extent of damage and casualty in a number of small islands in the Andamans group in the Indian Ocean is yet to be known, as rescue teams had not reached all the places.

Panic-stricken citizens of Port Blair ran out of their houses on Sunday morning as an earthquake of moderate intensity jolted the Andaman and Nicobar Islands.

The quake led to flooding of some areas in the city like Aberden Jetty area as well as some places in Nicobar Islands, official sources said.

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Almost the entire population of Port Blair was on the streets as the fire brigade advised them to stay outdoors in anticipation more tremors.

The tremor was part of a massive earthquake, which hit northern Sumatra in neighbouring Indonesia. Sumatra is about 1,500km from Port Blair.

Deol said that most of the 28 inhabited islands had been affected. "It is too early to estimate the exact extent of damage at this time."

The main jetty at Port Blair was severely damaged by tidal waves and the entire islands' maritime service being suspended.

The Port Blair airport, however, did not suffer any major damage. Even after the quake, two flights took off from there.

Rescue operations in all affected islands were hit because of the damage to the main jetty in Port Blair. Alternative arrangements were being made.

Most people on the island had gone to bed late on Saturday night after celebrating Christmas and the population was caught totally off-guard.

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Meanwhile, three Indian Air Force AN-32 aircraft on Sunday flew from Chennai and Bangalore airports carrying emergency and medical supplies to Andaman and Nicobar Islands, which was hit by an earthquake and tidal waves.

These will be the first aircraft to make contact with the islands, where several areas have been submerged. The islands are close to the epicentre of a major earthquake that rocked Sumatra Island in neighbouring Indonesia.

An IAF spokesman said the aircraft were headed for Port Blair and the Karnic airfield on the Andaman Islands. More aircraft have been kept on standby.

Though no SOS has been received from the Tamil Nadu, Andhra Pradesh and Orissa state governments, helicopters based in Hyderabad, Bangalore and Coimbatore have been placed on full alert to carry out emergency evacuation of civilians.

A naval spokesman said naval and coastguard ships have been placed on full alert all along the eastern coast to carry out rescue operations.