Emergency relief officials and doctors deployed to flood devastated communities in the Philippines Sunday to prevent outbreaks of disease as the death toll jumped to 85.
The flooding that submerged 80 percent of Manila early in the week has largely subsided but more than 150 towns and cities around the capital remain under water, affecting more than three million people.
Amid the ongoing relief operation, the weather bureau warned of a low pressure area developing some 850 kilometres (528 miles) to the east in the Pacific Ocean that could turn into a storm and bring more rain.
Many provinces around Manila remained inundated as overflowing dams continued to release water, the national disaster coordinating agency said.
Relief workers were dealing with "clogged pipelines and trash everywhere. Sanitation has emerged as a key problem," Red Cross secretary general Gwendolyn Pang told AFP.
"We have deployed health officers in evacuation centres and in flood-hit communities with the likelihood of diseases erupting."
The health department said water purification tablets were being distributed, while mass immunisations were being carried out to prevent an outbreak of diseases such as flu.
Of particular concern is a possible outbreak of leptospirosis, caused by exposure to water contaminated by rat urine, which infected 3,300 people and claimed some 250 lives in the aftermath of similar flooding in 2009.
"Many may have escaped the floods, but many could still die from leptospirosis or other diseases," Ramos said.
The Red Cross put up huge rubber bladder tanks for clean water, while local officials sent portable latrines to packed evacuation centres. Food packs were also rushed to some 770,000 people displaced by flooding.
Civil defence chief Benito Ramos said more than half of them were living in dire conditions in 948 evacuation centres -- mostly schools and churches converted into temporary shelter areas.
But in a town north of Manila, at least one family had set up camp on top of elevated tombs at a cemetery as they waited for aid, illustrating the extent of the crisis.
In all, more than three million people in 167 towns and 16 cities were affected by the heavy rains and floods, the disaster agency said.
"Many have returned to their homes as the waters subsided, but it is far from a normal situation," Ramos said.
"We are trying to help them return to their normal lives with a massive clean-up operation. There is muck everywhere, and it would take some time."
Ramos said the death toll rose to 85 on Sunday from 66 the previous day, with most of the casualties due to drowning.
The floods were caused by seasonal southwest monsoon that brought an unusual amount of rainfall over Manila and nearby areas, causing dams and river systems to overflow.
If the new low pressure disturbance develops into a major storm, it would bring more misery, Ramos warned.