More than 8,500 people were killed when giant waves triggered by a massive earthquake (8.9 on the Richter Scale, source: US Geological Survey), whose epicentre was near the Indonesian island of Sumatra, wiped out coastal areas in south and east Asia on Sunday morning.
It was the most powerful quake in 40 years.
Note: The toll is subject to change
In India, at least 1,500 died in Tamil Nadu alone as huge waves lashed the coastal areas, bringing in their wake death and destruction.
Shocked over the scale of the disaster, Prime Minister Manmohan Singh assured the affected states and Union territories of all possible assistance.
He also despatched Patil, Petroleum Minister Mani Shankar Aiyar and Communication Minister Dayanidhi Maran to the affected areas to help monitor the situation.
The Centre's Crisis Management Group met and drew up an emergency plan to carry out relief and rescue operations.
The army, air force and navy launched massive rescue and relief operations, pressing helicopters, transport aircraft and ships along the eastern coastline and in island territories to search for the dead and trapped.
This is the first time India has been hit by tsunamis, which are triggered by seismic disturbances -- coastal earthquakes, volcanic eruptions or undersea landslides -- that jolt the ocean floor. The result is a deep wave that stretches from the sea's surface to the floor and travels horizontally at speeds of up to 800 km/hr and rises between 50 and 100 ft.
According to reports, more than a million people were forced out of their homes in Sri Lanka.
Sri Lankan President Chandrika Kumaratunga declared a national disaster and the military was deployed to help rescue efforts.
Prime Minister Mahina Rajapakse's aide Lalith Weeratunga was quoted as saying, "We have are getting police reports from the main towns, but there are still areas where rescue workers have not been able to reach.".
The PM `has gone by helicopter to some of the areas which had been cut off', he added.
There were 1,032 fatalities in Batticaloa district, according to reports. In Trincomalee, there were reports of 320 deaths. The Galle resort town reported around 200 deaths.
Around 200 prisoners escaped when waves swept away a prison in Matara, in southern Sri Lanka.
Sri Lankan officials imposed a curfew as night fell, and tourists were being evacuated from the eastern coast to the capital, Colombo.
Rajapakse urged India to provide urgent medical assistance to his country and help with helicopters in the rescue mission.
India agreed and sent two naval ships to Galle, in the south, and Trincomalee. Indian aircraft will bring in relief supplies to the country on Monday.
Across Indonesia, Thailand and Malaysia, the toll was increasing by the minute. In Indonesia, many of the casualties were in the troubled Aceh region.
The tourist resorts of Thailand especially were filled with holidaymakers when the tragedy struck. Some 400 were killed on the island of Phi Phi. The resort town of Phuket witnessed 48 deaths.