The window was closing as search teams tried to rescue the dying victims of Haiti's earthquake before they become the dead, and governments around the world were rushing to get in aid supplies.
Several people, one of them a months-old baby who will be brought to the United States, were pulled alive today from the rubble.
But looting and violence were increasing, too, possibly jeopardizing rescue and aid distribution efforts.
The Haitian government said 20,000 bodies have been collected already, and officials expect the final number of victims from Tuesday's earthquake could reach 100,000, at a minimum.
At least 15 Americans were known to be dead, and late today the United Nations confirmed that its mission chief in Haiti, Hedi Annabi, died in the earthquake.
Haitian authorities estimated this morning that as many as one million people were homeless and 250,000 were wounded.
Amid the growing despair and desperation, President Obama enlisted his two presidential predecessors -- presidents George W. Bush and Bill Clinton -- to lead an American fundraising effort for Haiti.
"The country is in total chaos. The government is totally inexistent," Max Beauvoir, Haiti's high priest of Voodoo, wrote to ABC News' Jake Tapper in an e-mail. "Law and order no longer exist. ... How can the suffering ones expect to receive directly some humanitarian help?"
ABC News witnessed a violent street fight and spent time on a food line where tempers flared.
Seismic aftershocks continued to jolt Haiti, including a 4.5-magnitude event that shook Port-au-Prince and briefly halted rescue efforts this morning.
Some Haitians complained that foreign victims were being saved first -- particularly in light of multiple rescues from the rubble of the upscale Hotel Montana.
In many areas, families desperately searched for loved ones with only hand tools or whatever they had available.
One sign on a collapsed building said, "Welcome U.S. Marines. We Need Help. Dead Bodies."
Still, there was reason for hope, even four days after the main earthquake.
There were 26 international search and rescue teams on the ground in Haiti, U.S. officials said this morning. Four of them were American, and they had rescued at least 15 people as of the morning.
In addition, American rescue workers pulled Saint-Helene Jean-Louis, 29, from the rubble of the Port-au-Prince university later in the day.
And rescuers pulled another woman from her destroyed home this afternoon, though her eight children died.
Racing Against the Clock to Rescue Victims
"Search effort continues in full force," said Tim Callaghan, senior regional adviser for Latin America and the Caribbean at the Office of Foreign Disaster Assistance, who was spearheading U.S. operations on the ground.
"U.S. teams along with other international teams are continuing rescue efforts today and that will certainly continue [Sunday]," Callaghan added.
Late today, ABC News climbed through the remains of an apartment building where people said the voices of the survivors still could be heard.
From the rubble of an office building, a woman named Christine was signaling she was alive by clicking the remote control on her key chain and texting her friends.
At the Hotel Montana, searchers tried to save three more people trapped in the rubble Saturday afternoon -- one unconscious, but alive, and two women who were speaking, one in English, and another in French.
Even with all the frenzied activity and heroic rescues, there was no question that time was running out for all the trapped people.
And there was another massive time crunch -- the effort to get enough food, water and other aid material to desperate survivors in time to save them and prevent further looting and disorder.
Today was the first day that ABC News saw a significant presence of cranes, trucks and food deliveries, but it was not nearly enough.
Hillary Clinton: 'Here Today, Tomorrow and for the Time Ahead'
Secretary of State Hillary Clinton, who landed in Haiti shortly before 3 p.m., reportedly carrying supplies for U.S. embassy staff, said she and Haitian President Rene Preval discussed "all the priorities of the Haitian government and the Haitian people."
"We are focused on providing humanitarian assistance, food, water, medical help to those who are suffering," Clinton said. "We also are working with the Haitian government of the continuing rescue of those who can be rescued."
She later directly addressed the Haitian people.
"We are here at the invitation of your government to help you," she said. "As President Obama has said, we will be here today, tomorrow and for the time ahead. Speaking personally, I know of the great resilience and strength of the Haitian people. You have been severely tested, but I believe Haiti can come back even stronger and better in the future."
Doctors Without Borders: 'Never Seen So Many Serious Injuries'
But first came today.
Aid workers and doctors were trying to treat the wounded as supplies slowly got distributed, too slowly for the suffering people in this city who need so much.
Doctors Without Borders, which also goes by the French acronym MSF (Medecins Sans Frontieres), said its volunteers have been working "around the clock to treat the vast numbers of patients."
"Experienced MSF medical staff say they have never seen so many serious injuries," spokeswoman Emily Lindendoll said in a written statement, adding that doctors were working in bare-bones, improvised hospitals around the country, despite "little sign of significant aid distribution."
"The major difficulty here is the bottleneck at the airport, which has turned away a number of vital cargo flights," she added. "Lack of authorization to land at the airport has already caused a 24-hour delay of the planned arrival of MSF's much needed inflatable hospital."
Facing Death From Short Supplies
There was acute medical need at Champ de Mar, a burgeoning tent city of 5,000 earthquake refugees, including children, where ABC News' senior health and medical editor Richard Besser visited. Clean water was virtually non-existant there, food was a luxury and garbage littered every corner.
A two-story building fell on Pierre Michlet, 48, and he was stuck under the rubble for 14 hours. Blocks of concrete crushed his feet.
When Besser, a medical doctor, saw him, his bandage was dirty and risked becoming infected if not changed quickly -- minor first aid for someone who needed major care, but a risk for a life-threatening infection after several days.
"We don't have any antibiotics," Besser said. "What I would like to do is change his dressing, clean his wound, put on new medicine and pack it. But that's something we don't have."
A 3-month-old infant in the camp was not injured in the earthquake, but also faced potential death. The mother was feeding the baby sugar water because formula wasn't available, but babies fed sugar water can die of malnutrition.
Riding Along on an Aid-Delivery Mission
Despite the shortages at the camp, at least 180 tons of relief has landed in Haiti, U.S. officials said this morning. The government of Haiti has established 14 distribution points for aid, and five medical centers were up and running.
ABC News was able to ride along as aid workers from the World Food Program hoped to deliver 40,000 rations of high-energy biscuits, water tablets and pre-packaged meals. In the end, though aid got delivered, obstacles prevented the workers from even approaching their goal for the day.
For one thing, the scope of the disaster was so large that the aid group had to step up the delivery and include secretaries and other workers who did not normally load relief vehicles. Everyone from the office pitched in.
Soon, the strong aftershock caused volunteers to flee an already earthquake-damaged warehouse. Many refused to go back in for fear it would collapse.
After several hours the truck was loaded and finally on the way. A convoy was formed. U.N. security forces, including armored personnel carriers, accompanied the convoy through the streets to stave off the possibility of violence or a rush on the supplies.
The trucks rattled through Port-au-Prince, passing masses of people without shelter and food.
Four hours into the mission, they hit a roadblock of bodies. People began massing around the vehicles, desperate for supplies, saying, "We are hungry, we have nothing."
The truck found another way and at last, five and half hours after the trip began, the food was finally delivered at a local church, where mothers and children had been waiting all day, streaming in from a massive tent city nearby.
When the boxes were finally handed out, there seemed to be nothing but gratitude.
'All of My Family Is Dead ... I Have Nothing'
But even as aid started to move early today, the shock and grief in the aftermath of the earthquake already was turning to panic for many. In one shantytown, a water truck pulled up and people flocked to the back of the truck to get water for themselves and those in need.
"They are dying because nobody comes to help us," one man said.
"All of my family is dead," said another. "My mother is dead, my father is dead, my house is crushed; I have nothing."
The smell of decay has grown so strong from bodies littered through the streets and baking in the sun that people are putting toothpaste under their nostrils to help block the stench of death.
"We see the helicopters, and they do nothing," one Haitian complained.
"They're hungry," another man said of his fellow Haitians. "They don't have food. They don't have water. They don't have nothing."
U.S. Officials: Help Is on the Way
Officials insist more help is coming.
Callaghan said U.S. rescue teams will be working "nonstop." He declined to say when that effort will transition to a recovery operation.
Callaghan defined water as a top priority. The United States brought in water purification units Friday night and is donating one to the medical center being run by Argentina.
After the water purification units are up and running, officials expected 300,000 litres of water to be produced by the end of Saturday. Water also apparently was being brought in from the Dominican Republic.
U.S. troops have arrived -- 4,200 on the ground and on ships off the coast -- and thousands more are expected ashore by next week.
Despite being in Haiti for less than 24 hours, the carrier USS Carl Vinson has "contributed tremendously" in getting supplies to the airport and other landing zones, Navy Rear Adm. Victor G. Guillory told reporters in a conference call today. The 19 helicopters aboard the carrier are being used to deliver food, water and medicine.
This morning there were at least 20 sorties from the airport moving food and water to landing zones in the city near distribution nodes.
"The Navy is doing its best to flow material as quickly as possible ... getting better supplies to the people who need it," Guillory said. "I will tell you it will get better over time."
Because the port facilities at Port-au-Prince have suffered major damage, the Navy is sending the salvage ship USS Grasp, along with a complement of construction divers. The divers will see how extensive the damage is and whether some of the port facilities might be repaired. They're also looking at sending mobile piers.
American officials also are helping Haiti manage flights in and out of the damaged airport in Port-au-Prince.
In the longer term, the USNS Comfort, a floating hospital with a crew of 500 sailors, doctors and nurses, is expected to drop anchor outside Port-au-Prince this coming week, about nine days after Tuesday's earthquake.
According to the U.S. Navy, if the ship were on the ground in the United States, it would be the nation's biggest hospital. It has enough supplies and staff to treat 40,000 Haitians over the next several weeks, the ship's captain said.
Everyone on board has seen the pictures from Haiti.
"It has, at times, you know, been overwhelming emotionally," Lt. Cmd. Thomas Olivero said. "What's hard is to see everything that's going on over there and not being there. ... We will do everything we can. I mean, that's what we are going there for."
ABC News' Kate Snow, Chris Cuomo, Rachel Martin, David Kerley, Luis Martinez, Richard Besser and Christine Romo contributed to this report.