AFP - Despairing Haitians prayed in church ruins as rescuers raced against time to unearth quake survivors and the UN vowed to speed up desperately needed supplies of food, water and medicine.

The government said 70,000 bodies had been buried in mass graves since the 7.0 earthquake flattened much of the impoverished Caribbean nation on January 12, triggering a massive humanitarian crisis.

Officials fear the eventual death toll could top 200,000.

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Survivors were besieging hospitals and makeshift clinics, some carrying the injured on their backs or on carts, and violence flared as police tried to stop looting in a city market.

The stench of burning bodies hung over slums clinging to a Haitian hillside as residents abandoned the search for survivors and torched the squalid ruins.

Lieutenant-General Ken Keen, who is running the vast US military relief operation, said 200,000 might be a possible "start point" for the final death toll, but that it was too early to know.

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"Clearly, this is a disaster of epic proportions, and we've got a lot of work ahead of us," he said.

After hours of painstaking digging, a team from Florida unearthed a seven-year-old girl, a man aged 34 and a 50-year-old woman in the mangled wreckage of a supermarket in the ravaged capital Port-au-Prince.

Australian news crews reported putting aside their day jobs to rescue an 18-month-old baby after hearing her cries from underneath the rubble in Port-au-Prince as she lay trapped next to the bodies of her dead parents. Related article: Australia media crews rescue baby

"And then, out of the ruins came this little girl, and I will never forget it," Nine Network reporter Robert Penfold told The Australian newspaper.

"She did not cry. She looked astonished, almost as if she was seeing the world for the first time."

A Danish man was pulled unscathed from the flattened UN mission, but rescuers knew the likelihood of finding more survivors was waning with every hour.

"Today is the last day that I think we will be able to find survivors, mainly because of dehydration," said Rami Peltz, a rescuer with an Israeli team.

The church bells lay silent Sunday over the ruined capital, but the faithful still gathered in large numbers to pray for solace in the darkest hour of this deeply religious nation.

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"I want to send a message of hope because God is still with us even in the depths of this tragedy, and life is not over," said Father Henry Marie Landasse as he held mass in the rubble of the main cathedral.

But with vital supplies of water and food still struggling to reach some of those most in need, many Haitians were close to despair.

"Life is really hard, we have nothing," said 40-year-old Jean Osee, camped out with his family in front of the presidential palace in a makeshift slum of 50,000 wretched people.

"I don't have much strength to feed him, I can't look after him properly," Osee's daughter Louisoguine said, cradling her curly-haired baby.

Hundreds of rioters ransacked Hyppolite market in the heart of the capital. Police reinforcements descended on the market armed with shotguns and assault rifles and one rioter, a man in his 30s, was fatally shot in the head, an AFP photographer said.

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In the few medical facilities that are still standing in the city, there is not only a shortage of medication, but also of staff.

"They are overwhelmed and bursting at the seams," the International Committee of the Red Cross said.

The United Nations has estimated that the quake affected three million people -- one third of Haiti's population -- and left 300,000 homeless. Some 40 tent cities have sprung up in Port-au-Prince, according to the Red Cross.

Some 280 emergency centers will be set up from Monday to distribute aid to victims and provide shelter for the homeless, a Haitian government source said.

UN chief Ban Ki-moon vowed to accelerate aid efforts after flying over Port-au-Prince. "I am here to say we are with you. You are not alone. This is a tsunami-like disaster," he told a news conference.

Ban was to fly back to New York later Sunday bearing the bodies of some of the 40 UN staffers killed when the UN mission in Port-au-Prince collapsed, in what has become the global body's worst tragedy ever.

Canada announced that donor countries would meet in Montreal January 25 to discuss Haiti's reconstruction.

Lieutenant-General Keen promised to redouble efforts after the US military distributed 70,000 bottles of water and 130,000 food rations on Saturday.

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President Barack Obama mobilized military reserves, particularly medical staff to work on hospital ships. Another 7,500 military personnel were due by Monday to join 5,800 US forces already on the ground or in ships off Haiti.

On a visit to Haiti Saturday, US Secretary of State Hillary Clinton said: "As President Obama has said, we will be here today, tomorrow and for the time ahead."