Three days after Tuesday's earthquake, anger and frustration mounted in the ruined capital city, with thousands of people still desperate for food and water amid the stench of corpses left rotting in the tropical sun.
A vanguard of the 10,000 US troops being deployed to Haiti took control of the airport, clogged with tons of relief supplies, and began the first mass distributions of aid seeking to quell any threat of violence.
"As long as the people are hungry and thirsty, as long as we haven't fixed the problem of shelter, we run the risk of riots," warned Brazilian Defense Minister Nelson Jobim, after a visit to the capital Port-au-Prince.
Haitian officials said at least 50,000 people had been killed and 1.5 million left homeless in the Caribbean nation, one of the poorest countries in the world, which has long witnessed violence and bloodshed.
As UN officials on the ground pleaded for more medical and food aid for survivors, looting became widespread and there were angry scuffles at the few distribution points.
The fourth night after the quake brought fresh fears for many families already terrorized by armed gangs.
"Men suddenly appeared with machetes to steal money," said Evelyne Buino, a young beautician, after a long night in a neighborhood not far from the ruined city center. "This is just the beginning."
"We need to protect and guard (our home). There are many armed men, a lot of looting," said Eglide Victor, whose shabbily-built house was the only one left standing on his street in the heart of the Haitian capital.
Officials have estimated that some three million people -- a third of the population -- were affected by the 7.0-magnitude quake.
"We really need to focus on the living, and what we can do for them," said Nicholas Reader, spokesman for the United Nations Office for the Coordination of Humanitarian Affairs (OCHA).
UN chief Ban Ki-moon is set to visit Haiti on Sunday as the world body appealed for $562 million from donors. Ban said the UN system was mobilizing all its resources "as fast as we possibly can."
The UN mission in Haiti (MINUSTAH) was hit hard by the quake, with 37 of its 12,000 employees confirmed dead and 330 unaccounted for.
UN officials said the World Food Programme was now feeding around 8,000 people several times a day and hopes to feed roughly one million people within 15 days and two million people within a month.
"People had reserves for a few days, but now they are dwindling. They are afraid to go downtown in search of food because it has become too dangerous," said Haiti resident Patricia Etique, a Swiss citizen.
With thousands of bodies piled up on the streets of the capital, there was also a race against time to reach any survivors still in the ruins and treat those who were badly injured.
Foreign relief teams were increasingly seen on the streets, some backed by vital heavy-lifting equipment.
Scores more survivors were pulled alive from the rubble. A Belgian rescue team extracted a 28-year-old Haitian woman from one building after first amputating her leg above her right knee.
"We're very happy. It's what we're here for, and after this amount of time and the heat, it's great to still find people alive," Sergeant Major Edouard Dekoster, part of a specialized search and rescue team, told AFP.
US President Barack Obama finally reached Haiti's President Rene Preval by telephone Friday, and offered "full support" in earthquake relief aid and long-term rebuilding.
But President Preval told AFP that the aid operation needs to be better organised.
"We need international aid, but the problem is the coordination," he said.
Preval, whose temporary seat of government is now a police station near the capital's airport, said 74 planes from countries including the United States, France and Venezuela, had arrived in a single day.
Scientists warned that Haiti and its neighbors must prepare themselves for more massive quakes after the devastating tremors this week increased pressure along a lengthy fault line.
Paul Mann, a senior research scientist at the Institute for Geophysics at the University of Texas at Austin, warned that just because the rebuilding process had started people shouldn't assume the risk was over.
"This relief of stress along this area near Port-au-Prince may have actually increased stress in the adjacent segments on the fault," he said.
Keep up with the latest business news from the region with the Emirates Business 24|7 daily newsletter. To subscribe to the newsletter, please click here.