The official toll crossed 123,000 on Wednesday, but the true scale of the disaster may not be known for days, or even weeks, as rescuers struggle to reach stricken areas and grieving survivors searched for relatives.
"Entire villages have been washed away," according to Rod Volway, programme manager for Care Canada's emergency response team which was one of the first aid groups that went into Indonesia's northern Aceh province, the worst-hit area.
He added: "This isn't just a situation of giving out food and water. Entire towns and villages need to be rebuilt from the ground up. Everything has been destroyed."
Countries around the world sent rescue teams, food and millions of dollars in aid to the hardest-hit nations of Indonesia, Sri Lanka, India and Thailand to cope with the aftermath of the strongest earthquake in 40 years.
* Toll over 120,000
* Panic after India issues new tsunami alert and urges evacuation of coastal areas
* Millions scramble for food and clean water
* Aftershocks rattle Aceh
* Rescue and rebuilding will cost billions of dollars; 50 to 60 nations have given or pledged more than $220 million in aid
* WHO experts say Disease could kill as many people as tsunami
As the world pledged $220 million in cash and sent an international flotilla of ships and aircraft with hundreds of tonnes of supplies, history's biggest relief operation battled with the enormity of the task.
The United Nations said it was preparing to issue what could be its largest appeal for donations in its history to cope with its biggest and costliest relief effort.
Indonesian aircraft dropped food to isolated areas along the western coast of Sumatra, an island the size of Florida, where the tsunami obliterated entire towns.
US President George Bush said a pledge of $35 million in aid was just a start and that the 3rd Marine Expeditionary Force, based in Japan, would set up a forward command post in Thailand to coordinate efforts.
He announced on Wednesday that the US, Australia, Japan and India would form a "core group" to spearhead the international response to the catastrophe and urged other nations to join.
"This isn't just a situation of giving out food and water. Entire towns and villages need to be rebuilt from the ground up. Everything has been destroyed"
Care Canada's Rod Volway
The Pentagon is sending the USS Abraham Lincoln aircraft carrier, a helicopter carrier and a submarine to the region.
Countries from impoverished Cambodia to faraway Brazil have also joined in the relief effort.
Middle East countries such as Qatar and Saudi Arabia are also participating, announcing they were sending $10 million each.
Indonesia has suffered the biggest number of victims, with 52,000 estimated to be dead, although the toll could rise to 80,000 in Aceh alone, the province closest to the quake's epicentre.
In the provincial capital Banda Aceh, two aftershocks on Wednesday night woke nervous residents. Many people preferred to sleep outside.
Indian officials said their toll had hit 10,850.
In Sri Lanka, where nearly 23,000 people have been reported killed, many said there was still no sign of aid for ruined communities.
The tsunami is the world's biggest disaster since a cyclone killed 130,000 people in Bangladesh in 1991.