GENEVA - Rescue workers and relief goods started pouring into Haiti from around the world Thursday but aid groups were running into huge challenges trying to reach quake survivors trapped in the rubble or wandering homeless and hungry in the streets.
Ship deliveries were impossible to Port-au-Prince because the Haitian capital's port was closed by damage. Its airport was open but strained to handle a flurry of incoming flights carrying experts and aid.
Fearful of going near scores of quake-damaged buildings, Haitians stood or rested in the roads, slowing the transport of food and other crucial aid.
"It's chaos," U.N. humanitarian spokeswoman Elisabeth Byrs told The Associated Press. "It's a logistical nightmare."
Severe damage to at least eight Port-au-Prince hospitals made it nearly impossible to treat the thousands of injured or prevent outbreaks of disease, said Paul Garwood, spokesman for the World Health Organization.
Even as the United Nations stepped up its massive aid operation, the world body was trying to determine how many of its own staff were killed in the magnitude-7 quake that struck Tuesday.
"It's very difficult to give an exact number," said Byrs. "This is also a tragedy for the United Nations."
She said up to 100 U.N. staff were trapped in the main U.N. peacekeepers' building, which was destroyed.
Byrs said 40 search-and-rescue teams from around the world had started arriving in Haiti to look for survivors trapped inside collapsed buildings. But to find and save people, the rescuers will need heavy equipment to lift tons of rubble. Some teams have that equipment - including ones from Britain and Iceland - but many don't.
Although impoverished Haiti has virtually none of those machines, the neighbouring Dominican Republic does and can help meet the need, said Charles Vincent of the World Food Program.
"We'll have to see how that works out over the coming days," said Vincent. "The U.S. military will also be bringing in some equipment."
Some rescuers were bringing their own lifting equipment.
President Barack Obama announced the U.S. government was making initial $115 million relief effort and promised an all-out rescue and humanitarian effort including military and civilian emergency teams from across the U.S.
The aircraft carrier USS Carl Vinson was expected to arrive off the coast Thursday and the Navy said the amphibious assault ship USS Bataan had been ordered to sail as soon as possible with a 2,000-member Marine unit.
"We have to be there for them in their hour of need," Obama said.
U.S. Secretary of State Hillary Rodham Clinton and Defence Secretary Robert Gates cancelled plans to attend a meeting in Australia so that they could attend to the Haitian crisis.
The desperate situation has aid groups fearing a surge in lawlessness, Vincent said.
U.N. peacekeepers will be patrolling to try to control looting but they are dealing with many deaths and injuries of their own, he added.
The International Committee of the Red Cross said its forensic specialists would help ensure that the bodies are recovered and identified for the benefit of their families.
"There is a widespread myth that dead bodies may be the cause of epidemics in natural disasters," said ICRC forensic expert Ute Hofmeister. "This is not the case. The bodies of people that have died in a natural disaster do not spread disease, since they have died of trauma and not disease."
China dispatched a chartered plane carrying 10 tons of tents, food, medical equipment and sniffer dogs. Accompanying the emergency materials were a 60-member earthquake relief team that had firsthand experience in the country's own quake disaster two years ago.
The Red Cross estimated that some 3 million people will require aid, ranging from shelter to food and clean water, and said many Haitians could need relief for a full year.
The World Bank said it would provide $100 million in emergency aid to Haiti to support recovery and reconstruction work. Experts would be sent to assess the scope of the damage and help prioritize where needs are greatest.
Aid was delivered or promised from many countries, including Brazil, the European Union, Israel, France, Switzerland, South Korea and Canada.
The International Committee of the Red Cross has launched a dedicated Web site to help Haitians inside and outside the country to register and find missing loved ones.
Associated Press Writers Frank Jordans in Geneva, Meera Selva in London, Tini Tranh in Beijing, Kwang-tae Kim in Seoul, South Korea, Rod McGuirk in Canberra, Australia, Tran Van Minh in Danang, Vietnam, and Hrvoje Hranjski in Manila contributed to this report.