Tens of thousands of people are feared dead in Haiti's catastrophic earthquake, buried beneath demolished schools, hospitals and homes as traumatised citizens mill in streets strewn with rubble and scattered bodies.
As more than 30 aftershocks continued to shake the devastated capital Port-au-Prince, residents tried to rescue people trapped under rubble, clawing at chunks of concrete with bare hands.
An estimated 3 million residents are spending a second night without shelter in the shattered country.
The UN chief said 16 UN personnel were confirmed dead late Wednesday in the earthquake that decimated Haiti's capital, with 100 to 150 UN workers still unaccounted for, including the mission chief and his deputy.
Secretary-General Ban Ki-moon announced that 11 Brazilian peacekeepers and five international police officers - three from Jordan and one each from Chad and Argentina - were killed in the "horrendous" quake.
UN officials said 56 others were injured. Seven who were seriously hurt were evacuated from the country, they said.
"Many continue to be trapped inside UN headquarters and other buildings," said Ban, noting that includes the UN's mission chief, Hedi Annabi, and his chief deputy, Luis Carlos da Costa. "Other peacekeepers and civilian staff from many member states remain unaccounted for."
UN peacekeeping chief Alain Le Roy said at least 10 people were pulled alive on Wednesday from the lower floors of the five-story headquarters building for the UN peacekeeping mission, which collapsed in Tuesday's magnitude 7.0 earthquake quake.
Earlier on Wednesday tens of thousands wandered dazed and sobbing in the chaotic, broken streets, hoping desperately for assistance.
One young man yelled at reporters in English: "Too many people are dying. We need international help ... no emergency, no food, no phone, no water, no nothing."
Bodies were visible all around the hilly city: under rubble, lying beside roads, being loaded into trucks.
Asked by a CNN reporter how many people had died, President Rene Preval replied "I don't know," adding "up to now, I heard 50,000 ... 30,000."
But Preval did not say where the estimates came from.
The local Red Cross - used to dealing with disaster in a country long dogged by poverty, catastrophic natural disasters and political instability - said it was overwhelmed.
Preval called the damage "unimaginable" and described stepping over dead bodies and hearing the cries of those trapped in the collapsed Parliament building, where the senate president was among those pinned by debris.
Destruction in the capital was "massive and broad," and tens - if not hundreds - of thousands of homes were destroyed, a spokesman for the UN mission said.
THE DEATH TOLL
Mr Ban said he was immediately dispatching Assistant Secretary-General for Peacekeeping Edmond Mulet, who was Annabi's predecessor in Haiti, to Port-au-Prince to take over as acting chief of the UN mission and co-ordinate the international emergency aid effort.
The UN chief said Mulet would arrive Thursday morning and hold immediate meetings with Haiti's President Rene Preval and Haitian officials.
"Most urgently is the emergency search and rescue: People buried under the rubble are still alive. We must save them, as many as possible, and we must move immediately,'' Ban said. ''To the people of Haiti, I say this: We are with you. We are working quickly, as fast as humanly possible."
Ban said one Chinese and at least two US search and rescue teams should have arrived in Haiti by Wednesday night (Thursday evening, local time), with two more US teams expected to arrive soon after. He said Mullet would try to meet with Haitian President Rene Preval and other government leaders immediately after his arrival. Ban said his office was unable to directly contact Preval.
Ban's former spokeswoman, Michele Montas, a well-known Haitian journalist, was visiting family when the quake struck. In an e-mail received by UN staff late Wednesday afternoon, Montas said she was OK but Port-au-Prince ''is 80 percent destroyed,'' said Montas' successor, UN spokesman Martin Nesirky said.
"Saw hundreds of bodies in the street this morning and people trying to reach survivors under buildings and carrying the wounded on doors and makeshift stretchers. Most everything above one-story has been leveled," and there have been ''more than 30 aftershocks,'' Montas wrote in an e-mail.
Former NZ Prime Minister Helen Clark, head of the UN Development Program, said 38 UNDP staff are unaccounted for, including 10 believed to have been in the building adjacent to the agency's main office, which collapsed.
The UN's Haitian mission - spread across the country - includes 7,000 peacekeeping troops, 2,000 international police, 490 international civilian staffers, 1,200 local civilian staffers and 200 UN volunteers, he said. The force was brought in after a bloody 2004 rebellion following decades of violence and poverty in the nation.
Le Roy said the 3,000 troops and police in Port-au-Prince are securing the airport and port, patrolling, and helping to clear roads in addition to digging in the rubble of the collapsed headquarters building.
The UN is operating out of its logistics base near the airport, which was not seriously damaged, he said.
Meanwhile in the city scattered bodies were laid out on sidewalks, neatly wrapped in sheets and blankets. Voices cried out from the rubble.
"Please take me out, I am dying. I have two children with me," a woman told a journalist from under a collapsed kindergarten in the Canape-Vert area of the capital.
The presidential palace lay in ruins, its domes fallen on top of flattened walls. Preval and his wife were not inside when the quake hit.
The quake's epicentre was only 16km from Port-au-Prince. About 4 million people live in and around the city and many slept outside on the ground, away from weakened walls, as aftershocks as powerful as 5.9 magnitude rattled the city. One strong aftershock sent guests running in panic from the already damaged Villa Creole hotel on Wednesday afternoon.
"We have a lot of people here that need help. They need food, water," said Vanessa Charlamagne, 27, a Haitian-American lab technician visiting from Maryland, who spent the night with hundreds of others on the grass of a park near the palace.
"They spent the whole night praying and praying, it was like a nightmare," Charlamagne said. An elderly woman died of apparent shock as she lay nearby in the park overnight, while another woman gave birth to a baby boy, she added.
Haitian Red Cross spokesman Pericles Jean-Baptiste said his organisation was overwhelmed and out of medicine. "There are too many people who need help ... We lack equipment, we lack body bags," he told Reuters.
Normal communications were cut off, roads were blocked by rubble and trees, electric power was interrupted and water was in short supply. The only lights visible in the city came from solar-powered traffic signals.
The poorest country in the Western Hemisphere, Haiti is ill-equipped to respond to such a disaster, lacking heavy equipment to move debris and sufficient emergency personnel.
RESCUERS EN ROUTE
One of the city's best-known hotels, the Montana, had collapsed, said Haitian businessman Manuel DeHeusch, a tile factory owner, who added the hotel owner, his aunt, had died buried in the rubble
"I am appealing to the world, especially the United States, to do what they did for us back in 2008 when four hurricanes hit Haiti," Raymond Alcide Joseph, Haiti's ambassador to Washington, said in a CNN interview.
US President Barack Obama called the quake an "especially cruel and incomprehensible" tragedy and pledged swift, co-ordinated support to help save lives. The Pentagon was sending an aircraft carrier and three amphibious ships, including one that can carry up to 2,000 Marines.
US Secretary of State Hillary Clinton said she had decided to cancel the remainder of her trip to the Pacific and to return to Washington because of the earthquake in Haiti.
Medical aid group Doctors Without Borders said its three hospitals in Haiti were too badly damaged to use, and it was treating the injured at temporary shelters.
"What we are seeing is severe traumas, head wounds, crushed limbs, severe problems that cannot be dealt with with the level of medical care we currently have available," said Paul McPhun, operations manager for the group's Canadian section.
The University of Miami School of Medicine sent a plane full of doctors and nurses to set up a field hospital.
The World Bank pledged an additional $100 million. The United Nations said $US10 ($NZ13.5) million would be released immediately from the its central emergency response fund and it would organize a flash appeal to raise more money.
HOUSES TUMBLED, CARS BOUNCED
The United States, China and European states were sending reconnaissance and rescue teams, some with search dogs and heavy equipment, while other governments and aid groups offered tents, water purification units, food and telecoms teams.
The quake hit at 5pm Tuesday local time (11am Wednesday, NZ time), and witnesses reported people screaming "Jesus, Jesus" running into the streets as offices, hotels, houses and shops collapsed. Experts said the quake's epicentre was very shallow at a depth of only 10km, which was likely to have magnified the destruction.
Witnesses saw homes and shanties built on hillsides tumble as the earth shook, while cars bounced off the ground.
Haiti's cathedral was destroyed and media reports said the archbishop of Port-au-Prince, Monsignor Joseph Serge Miot, had been found dead in the wreckage of the archdiocese office.
NZ FAMILY IN COLLAPSED HOTEL
Kiwi woman Emily Rejouis, desperately searching for her family in earthquake-devastated Haiti, has managed to get her youngest daughter, Alyahna, out of the rubble alive.
It is understood the daughter, 2, was found under the body of her father Emmanuel, and has a broken leg, Radio New Zealand is reporting.
Her husband Emmanuel is believed to be dead while her two other daughters, Zenzie and Kofie-Jade are still buried under toppled buildings after an earthquake struck the capital of the impoverished Caribbean country yesterday.
Emily Rejouis, originally from Nelson, rang her step-sister Caroline Larnach in Auckland last night on a borrowed satellite phone amid the chaos in Haiti because there were no emergency services on the ground.
An emotional Ms Larnach said the family was desperate to get help to find her step-sister's family.
"We're just absolutely desperate to have some help for our family. We're just absolutely distraught with what's happening.
"We need support from the New Zealand Government and from any services that are represented in Haiti."
Ms Rejouis had returned from the collapsed United Nations building to the Karibe Hotel in Port-au-Prince, to find it a pile of rubble.
Nine Australians known to be in Haiti are safe, but fears remain for others.
Australian aid worker Ian Rodgers says the earthquake struck with "extreme force and ferocity".
"What's resulted is a lot of landsliding, and buildings have collapsed and then fallen down the hillside," he told Network Ten from Port-au-Prince.
"Electricity is now off. We have had reports hospitals are damaged and destroyed. We're trying to find out what is functioning and what is not functioning."
Mr Rodgers - Save the Children's senior emergency adviser - said he could hear people pleading for help.
"There's a lot of distress and wailing of people trying to find loved ones who are trapped under buildings and rubble."
- Reuters, AP with MICHAEL FOX , Stuff.co.nz and NZPA