Tens of thousands of flash flood survivors in the Philippines face life in tent cities for months while safe areas to resettle them are sought, top relief officials said Monday.

More than 60,000 people displaced by tropical storm Washi are sheltering in government buildings in Cagayan de Oro and Iligan cities, most of them in schools that reopen after the holidays, civil defence chief Benito Ramos said.

"We can't construct permanent shelters for them immediately. It will take some time. They have to move into tents when schools reopen on January 3," he told AFP.

Floods unleashed by the storm obliterated entire communities on the main southern island of Mindanao on December 17, many of them shanty towns built on sandbars which were swept out to sea as their poor migrant inhabitants slept.

Manila does not normally build houses for those left homeless by natural disasters, but President Benigno Aquino has banned the victims from returning to flood-prone areas, stationing armed police to enforce the measure.

Social Welfare Secretary Corazon Soliman said army engineers were building temporary bunkhouses and latrines in Cagayan de Oro, which accounted for half the 1,236 officially confirmed deaths.

More would be built in Iligan once the local government found a suitable relocation area, she added.

"The target is to have transition shelters and bunkhouses in the first two weeks of January so families can feel some personal space that they can't get at evacuation centres," she told ABS-CBN television.

But at just 12 units each there will not be enough space for all the displaced and the rest would have to stay in tents, she added.

Ramos said there was no definite timetable for building permanent houses, but he expected some to be ready in six months.

Evacuees said they feared for the future.

At a Cagayan de Oro gym packed with about 300 families, Fede Mendez said she and her jobless husband had sent their two young children to live with her cousin while they wait for government housing slots.

"We're back to zero. We don't have any money nor jobs, so we'd take whatever the government offers us," she told AFP.

Every available space inside the building is filled with mats and cardboard boxes, and Ali Tongson, a local relief worker, said the toilet facilities were insufficient.

Cagayan de Oro Mayor Vicente Emano said that Manila's promised funding for the shelters was not enough, and cast doubt on suggestions that the displaced could work on the permanent housing projects.

"I don't know if these people can build their own houses, considering that they've lost everything," he said.

Local officials have reported more than 1,000 people missing from the floods, a figure that Ramos considers possibly overstated.

Many of the dead remain unidentified and unclaimed at overflowing local mortuaries, while military reservists called up to help deal with the emergency are clearing away mud and debris from the disaster.

The focus of the search has shifted to the sea, where bloated bodies lie scattered in debris-strewn bays.

"The search is tapering off. The problem is there could still be bodies buried under the uncollected debris in the cities," Ramos said. "There's no Christmas here. It's a sad spectacle."