"I can not begin to imagine the horror that went through the families and all of the people who heard this noise and then had their lives snuffed out by this wave," Powell said Wednesday after flying over flattened villages along Sumatra's northern coast, which was home to two-thirds of the nearly 150,000 killed across Asia.
"I've been in war and I've been through a number of hurricanes, tornadoes and other relief operations, but I've never seen anything like this."
So far $2 billion has been pledged to relief efforts in 11 countries hit by the Dec. 26 quake off the western coast of Indonesia that triggered waves causing deaths as far away as East Africa.
Requests for more U.S. aid keep coming, reports CBS News Correspondent Lee Cowan. The United Nations has asked for the use of at least four C-17 cargo aircraft, which can transport over 65 tons and are able to land on short runways.
The challenges are enormous, with millions homeless and threatened by disease. The United Nations said it will build camps on Sumatra for up to 500,000 people.
Haggard, dehydrated tsunami survivors have been flooding hospitals. Psychologists were struggling to help children cope with unspeakable tragedy. Aftershocks added to the threats, with another strong quake felt Wednesday, rattling the region but causing no known injuries.
Powell was one of the first to arrive in Indonesia, where the international conference on tsunami aid is to be held Thursday in Jakarta. Powell and the other representatives at the conference will discuss coordinating relief efforts and the need to build a tsunami warning system for the Indian Ocean. One already exists in the Pacific.
As he arrived in Banda Aceh, Indonesia, Wednesday, Powell stood at an altitude of a few hundred yards and saw not a tree or building standing along the coast. City block after city block in the tsunami-devastated city was transformed by the tidal wave, which in one neighborhood, left a large ship lying on its side, half submerged in water and mud.
The former U.S. army general said he saw "how the wave came ashore, pushing everything in its path - cars, ships, freighters overturned - all the way up to the foothills, and then starting up the foothills until finally the waves came to a stop."
Money has poured in from around the world, the largest share from Japan.
"I think Japan must do as much as it can to help," Prime Minister Junichiro Koizumi said, calling for companies in the world's second-largest economy to respond with donations to the kind of disaster seen "only once a century."
Even impoverished North Korea has chipped in - with a pledge of $150,000. Convicts in Malaysia are donating money earned doing prison work, and war-torn Afghanistan plans to send doctors.
Powell is leading a fact-finding mission for President Bush along with Mr. Bush's brother, Florida Gov. Jeb Bush. The two, whose mission is to figure out how to best focus U.S. aid for the tsunami zone, got their first glimpses of destruction Tuesday as they toured the Thai resort of Phuket.
At the town hall in Phuket - a popular tourist destination for Europeans and Americans - Powell and Bush saw scores of photographs and posters posted outside the town hall seeking information on missing tourists.
Powell's airplane flew slow and low on the in, giving him a close view of flattened houses and ruined beaches.
Powell toured an office where American forensic experts are helping Thai officials identify thousands of bodies that washed ashore and said afterward he will recommend expanding U.S. forensic assistance.
Thailand's foreign minister, Surakiart Sathirathai, said told the U.S. delegation that the thing the Thai government would welcome U.S. technical assistance to build an early warning system to guard against tsunamis in the Indian Ocean and South China Sea.
"We'll do everything we can to contribute," said Powell.
Discussing U.S. aid in general, Powell said, "The United States has made a significant financial contribution, but we have done much more than that." He cited millions of dollars raised in private donations in the United States even before President Bush announced Monday in Washington that his father, the first President Bush, and former President Clinton, will spearhead a fund-raising drive.
Powell also noted the massive U.S. military assistance now swinging into high gear that is delivering food, water and supplies and evacuating wounded.
"I think we have demonstrated in recent days our willingness to provide support, not only financial support - but the military support that our Pacific Command is now providing," he said.
"We are in solidarity with you as you deal with this crisis," Powell said in Bangkok Tuesday. "The aftermath of the tsunami is a tragedy for the entire the world, and the United States will certainly not turn away from those in desperate need."
Jeb Bush also spoke of solidarity with tsunami victims, noting that his home state of Florida was battered by four hurricanes in 2004.
"We share this experience," said the Florida governor, emphasizing that the American people want to offer a helping hand.