Rescue teams racing against the clock in Haiti's ruined capital have found already nightmare conditions compounded by widespread insecurity that forces them to stop work at nightfall.

The World Food Program said its warehouses in Port-au-Prince had been looted and that it would have to restock in order to feed survivors.

Sporadic gunfire is echoing across the capital, as survivors of Tuesdays massive earthquake endure a third night on the streets with little food, water or medical supplies.

Anger and despair is mounting in Port-au-Prince, with rotting bodies littering the streets and little sign of desperately needed international aid for the three million people affected by the disaster.

Much of the aid remains at the Haitian capital's airport and some relief workers and officials say they are too scared to leave the security of the airport until day breaks.

Many on the ground say security is desperately needed, as most of the most members of the city's police force are busy searching for their own relatives.

"Our biggest problem is insecurity. Yesterday they tried to hijack some of our trucks. Today we were barely able to work in some places because of that," Delfin Antonio Rodriguez, Civil Defence chief and rescue commander for the Dominican Republic, said.

"There's looting and people with guns out there, because this country is very poor and people are desperate."

Deepening the volatility in the city, Haiti's main prison was partly destroyed, allowing thousands of prisoners to escape.

Lieutenant General PK Keen, who heads the US relief operation in Haiti, on Friday said he was "cognisant of the increasing concerns about security."

"Up to this point, we have not seen a great deal of insecurity, but clearly that is a concern, and we will work with the government and the national police to deal with it as best we can," he told CNN from the Port-au-Prince airport

Troops on the way

As part of its aid effort, the United States is sending in more than 5,000 troops.

North America correspondent Lisa Millar is embedded aboard the US aircraft carrier USS Carl Vinson, which is ready to sail for Haiti from the Guantanamo Bay naval base.

One of the questions over the USS Carl Vinson's deployment is that what is probably more needed is the comfort hospital ship that still sits off the coast of Baltimore in the north east United States.

It will apparently not arrive off Haiti for another week.

There has been some suggestion the US been slow to act, but the military and logistical challenges are extraordinary.

Some of the injured are already being brought to Guantanamo Bay, with up to 24 people being airlifted there and treated in the past 24 hours.

US State Department spokesman PJ Crowley says eight search-and-rescue teams with a total of 260 people are on the ground in Port-au-Prince and 30 countries have pledged or already sent help.

China, France, Iceland, the US and Venezuela are among those with teams in situ.

"Not only is the United States's commitment to Haiti growing, but also the international commitment as well," Mr Crowley said.

The US had also taken over air traffic control at the swamped airport which was now operating around the clock, he said. However, flights were delayed as staff struggled to unload supplies.

Haitians were also angered they had had no word from their leaders.

'Nothing is coming'

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

"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," said Jean-Baptiste Lafontin Wilfried.

Despite the launch of the massive aid operation, there is no sign of heavy-lifting equipment among the rubble even as tons of material and badly needed supplies flooded the airport.

The rapidly decomposing bodies are also posing a major problem.

Port-au-Prince resident Jacky Dodard says corpse disposal has been random and chaotic.

"What is happening is that there is no help in the streets. Personally, I haven't seen any help," she said.

"So everybody is trying to drop their dead bodies somewhere. They don't know what to do with the dead bodies."

Haitian officials have warned the overall death toll may top 100,000 as a result of the powerful quake that ripped across the poorest nation in the Americas.

The International Red Cross said the quake, the largest in the Caribbean island nation in more than 150 years, has killed between 40,000 and 50,000 people.

"If international aid doesn't come, the situation will deteriorate quickly. We need water and food urgently," said Haitian survivor Lucille, still dazed by the scenes of devastation and carnage.

'More doctors, fewer journalists'

Witnesses say there has already been some looting in the city.

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

Haitian native and hip hop star Wyclef Jean has described conditions as "the apocalypse" and said Haiti needed to raise $1 million a day to survive.

"We spent the day picking up dead bodies. All day that's what we did. There's so much bodies in the streets that the morgues are filled up, the cemeteries are filled up," he told Fox News.

Doctors were struggling to treat the vast numbers of sick and injured, with medical charity Medecins Sans Frontiers speaking of patients with "severe traumas, head wounds, crushed limbs" and burns.

The United Nations says 36 of its staffers had been killed in the worst disaster in the global body's history. Another 188 were still missing.

US President Barack Obama sought to lift up a despairing people, who face acute shortages of food, water and shelter, offering $US100 million 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.

Mr Obama and French President Nicolas Sarkozy, along with Brazil and Canada and other concerned nations, are planning to hold an international conference on Haiti's reconstruction, the French president's office said.

"People throughout the world want to help," said UN chief Ban Ki-moon.

"One of our biggest challenges will be to help them to help Haiti to the utmost," he said.

- ABC/AFP