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Bullit Marquez, Associated Press
Flood-affected residents queue up for relief goods being distributed at an evacuation center Thursday, Dec. 22, 2011 following the last Friday's flash flooding brought about by Tropical storm Washi in Cagayan De Oro city, southern Philippines. Tens of thousands of residents continue to be housed in evacuation centers in the two cities of Cagayan De Oro and Iligan after the floods that killed more than a thousand people and washed away their homes.

ILIGAN, Philippines — Two southern Philippine cities devastated by flash floods that killed more than 1,000 people look like they have been hit by a tsunami, a United Nations official said Thursday as he appealed for $28 million in aid to help half a million people affected by the disaster.

U.N. humanitarian coordinator Soe Nyunt-U also voiced concern about the possibility of disease outbreaks among the thousands living in evacuation centers after their houses were washed away last Friday when a tropical storm unleashed flash floods.

"It was as if the cities were hit by an inland tsunami," Nyunt-U told reporters in Manila. "Entire areas were completely flattened. Only a few sturdy buildings remain standing, and these had sustained a lot of damage."

"Debris from houses, buildings and other structures that had been destroyed by the storm was all swept out to the sea, leaving huge areas devoid of all traces of habitation," he said.

Nyunt-U said he was hopeful donors and foreign governments will respond to the appeal despite the global economic crisis. An appeal launched following a 2009 typhoon that killed about 500 people in Manila collected only half the funds needed.

"It's the Christmas season and the willingness of the international community is high," he said, adding that "no country can stand alone."

About 45,000 displaced are inside evacuation centers, most of them in worst-hit Iligan and Cagayan de Oro cities in the southern Mindanao region. Another 266,000 are being assisted outside temporary shelters. Nearly 30,000 houses were destroyed and damaged. The two cities are home to nearly a million people.

Local authorities and grieving relatives were moving ahead with dozens of burials each day, after a handful of funeral parlors complained they were overwhelmed and could no longer accept bodies, which were still being retrieved from the sea or mud almost a week after the disaster struck.

Aid workers rushed in relief supplies, but a lack of running water was a major concern.

"We must improve this situation at the soonest possible time to avoid disease outbreaks that will further compound the hardships of the people already weakened by hunger and grief from loss of family and friends," Nyunt-U said.

He mentioned a cholera type virus that may occur due to problems stemming from congestion in the evacuation centers, where poor sanitation and hygiene posed a health risk.

Associated Press writers Hrvoje Hranjski and Teresa Cerojano in Manila contributed to this report.