By Beatriz Lecumberri and Stephane Jourdain

PORT-AU-PRINCE, Jan 14, 2010 (AFP) - Anger and despair mounted in quake-hit Haiti Thursday with scores facing a third night trapped beneath the ruins, food and water running out, and little sign of international aid.

The stench of death hung over the capital of Port-au-Prince as residents hunkered down for another sleepless night in the open, traumatized by the aftershocks still rocking the nation after Tuesday's 7.0 earthquake.

Despite a massive aid operation, there was no sign of heavy lifting equipment on the streets of the city with tonnes of material and badly-needed supplies apparently jammed at the international airport.

Officials have warned the overall death toll may top 100,000 and say three million people could have been affected by the powerful quake that ripped across the poorest nation in the Americas.

"If international aid doesn't come, the situation will deteriorate quickly.

We need water and food urgently," said Lucille, still dazed by the scenes of devastation and carnage on the Caribbean island nation.

Sporadic gunshots were heard, and witnesses said there had already been some looting in a city that has seen bloodshed and violence over the past decades.

"More doctors, fewer journalists," one man yelled out angrily, shaking his fists at a foreign media crew.

China, France, the United States and Venezuela already have some aid teams on the ground, with Washington sending ships, helicopters, planes, rescue teams, a floating hospital and more than 5,000 troops.

But little had yet been deployed, and Haitians were also angered that they had had no word from any of their own leaders.

One group trying to free a man trapped in the rubble of the tax office looked up wearily at the planes flying overhead.

"I can't understand what they are doing, where they are going," said Jean-Baptiste Lafontin Wilfried as US Coast Guard planes sliced through the skies.

"We hear on the radio that rescue teams are coming from the outside, but nothing is coming. We only have our fingers to look for survivors," he said.

Within just a few hours, the airport, where the control tower was damaged, was forced to appeal for a temporary halt in aid flights because the runway and ramp area was clogged.

It was a blow to aid organizations in their race against time to reach the thousands still believed to be trapped.

More than 48 hours after the quake, Haitians were still digging by hand through mountains of concrete and rubble while the screams and moans of those buried below rang out.

Dozens of people were rescued thanks to frantic efforts and as sniffer dogs began to comb the ruins. They included Estonian police officer Tarmo Joveer pulled virtually unharmed from the rubble of the UN headquarters by a specialized US rescue team from Virginia.

But the moments of joy were few, compared to the death and destruction stalking the city.

"It's a small miracle," UN chief Ban Ki-moon said at the United Nations in New York, as he revealed that 36 UN staffers had been killed, in the worst disaster in the global body's history.

US President Barack Obama sought to lift up a despairing people, facing acute shortages of food, water and shelter, offering 100 million dollars in immediate assistance.

"To the people of Haiti, we say clearly and with conviction, you will not be forsaken, you will not be forgotten," he said.

A planeload of 50 Chinese soldiers, clad in orange jumpsuits, had flown into the airport at first light bringing with them three sniffer dogs, swiftly followed by two teams of French firefighters also backed by trained dogs.

"People throughout the world want to help," said Ban.

"One of our biggest challenges will be to help them to help Haiti to the utmost," he said, as communications remained poor, and moving around was hampered by destroyed roads and lack of gasoline.

A first contingent of US troops was headed to Haiti, and the USS Carl Vinson aircraft carrier was to arrive later in the day with destroyers and more Coast Guard ships en route and 5,000 troops on stand-by.

But lacking heavy lifting equipment, harrowing scenes were being repeated across the city as frustrated workers dug with hands and simple tools to reach the trapped.

Some people had set up temporary shelters with sheets and covers in a public square, while others were trekking out carrying meagre belongings, searching for safer places outside the city.

Casualty figures were impossible to calculate, although Haitian Prime Minister Jean-Max Bellerive said the final death toll could be "well over 100,000."

US Secretary of State Hillary Clinton, who canceled an Asia trip and returned to Washington, said the death toll would reach "tens of thousands."

Former US president Bill Clinton, a United Nations special envoy to Haiti, warned of an unprecedented humanitarian disaster.

Early estimates were that "nearly three million people " almost a third of Haiti's population - may need aid, making this one of the great humanitarian emergencies in the history of the Americas," he said.