The scale of devastation wrought by sea surges that killed about 23,000 people on Asia's shores is starting to emerge.
Around a million are now homeless in Sri Lanka
The death toll is still climbing, thousands are missing and millions have been made homeless by the world's worst earthquake in 40 years.
At least 10 countries have been affected, with Sri Lanka, Indonesia, India and Thailand among the worst hit.
International aid efforts have begun amid fears that disease could spread through the disaster zone.
Survivors may have little clean water or sanitation after Sunday's 9.0 magnitude earthquake sent huge waves from Malaysia to Africa.
Many places are still affected by flooding and communications remain disrupted, with contact not yet made with some remote regions.
The United Nations says the international relief operation is likely to be the biggest in history.
Though it was not the biggest tsunami wave ever recorded, "the effects may be the biggest ever because many more people live in exposed areas than ever before", said UN emergency relief co-ordinator Jan Egeland.
He said the relief operation would probably cost "many billions of dollars".
Digging for the dead
Communities were swept away and homes engulfed by waves up to 10m high after the quake created a wall of water that sped across the oceans.
The number of dead has climbed well into the thousands in Sri Lanka, India and Indonesia, and thousands are feared to have been killed on the Andaman and Nicobar islands, where reports say several islands have been submerged.
In northern Indonesia, nearest to the epicentre of the undersea quake, the vice-president said he feared fatalities in the worst-hit province of Aceh could rise as high as 20,000.
Jusuf Kalla appealed for urgent international aid.
"It's very, very bad," he told reporters after a trip to the area. "We need help fast."
Click below to see how the disaster unfolded
Packed holiday resorts in Thailand were also badly hit, and walls of water killed people in Malaysia, the Maldives, Burma and Bangladesh.
Waves also swept the Somali coastline after nightfall on Sunday, where hundreds are feared drowned and thousands made homeless, officials said.
In Sri Lanka, about a million are now homeless.
The BBC's Roland Buerk in the southern town of Galle says people all along the coast have been digging - for food, water, belongings - and the dead.
Searches have also been continuing off southern India for those swept away from beaches or in fishing boats.
Schools and temples have been converted into shelters along the coastal belt, but correspondents say they are already overcrowded.
1960 - Chile, 9.5 magnitude
1964 - Alaska, 9.2
1957 - Alaska, 9.1
1952 - Russia, 9.0
2004 - Indonesia, 9.0
Thai officials doubled the death toll as rescue teams said foreign tourists from 13 countries were among those killed.
A national disaster has been announced in the low-lying Maldives islands, more than 2,500km (1,500 miles) from the quake's epicentre, after they were hit by severe flooding.
UN teams are on their way to Sri Lanka and the Maldives to assess immediate priorities.
Sri Lanka says it urgently requires several million water purification tablets, food, tents and blankets as well as medical supplies.
International organisations and countries have already made pledges to help the victims.
- The International Monetary Fund promised "whatever possible assistance"
- The Red Cross launched an appeal for 5m euros (£3.5m; $6.8m)
- The European Union pledged 3m euros (£2.1m; $4.1m)
- The US promised $15m (£7.8m)
- Australia pledged 10m Australian dollars (£4m; $7.7m) and sent two planes carrying drinking water and purification equipment to Indonesia
- Russia sent 25 tons of humanitarian aid to Sri Lanka
- The UK was due to send a plane to Sri Lanka with plastic sheeting and tenting
- France sent a plane with 100 rescue workers, doctors and five tonnes of aid to Sri Lanka. The French Foreign Minister was to accompany another aid flight.
Sunday's tremor - the fifth strongest since 1900 - had a particularly widespread effect because it seems to have taken place just below the surface of the ocean, analysts say.
Experts say tsunamis generated by earthquakes can travel at up to 500km/h.
IMPACT OF THE EARTHQUAKE