People negotiate a flooded road in Baseera in Pakistan's Punjab province on Monday. The UN estimates the floods that began in July have affected more than 17 million people. (Aaron Favila/Associated Press)

Recovering from the floods still battering Pakistan will take at least three years, President Asif Ali Zardari said as the waters swept south after leaving millions homeless.

The floods that began nearly a month ago with hammering monsoon rains in the northwest have affected more than 17 million people, the United Nations estimates. Most of the more than 1,500 deaths occurred early in the flooding, but the crisis is still growing.

Zardari defended the government's much-criticized response to the unprecedented floods but acknowledged recovery will take a very long time.

"Three years is a minimum," Zardari told reporters Monday in the capital, Islamabad.

The widespread misery caused by the floods has triggered worries about social unrest, food riots or even a challenge to the government's rule.

Local charities, the Pakistani army and international agencies are providing food, water, medicine and shelter to the displaced, but millions have received little or no help. Aid officials warn that widespread outbreaks of waterborne diseases such as cholera now pose a threat.

Disease outbreaks possible

Dr. Jahanzeb Orakzai, Pakistan's national health co-ordinator, said a team has been formed to oversee the response to any health emergencies and includes international groups such as the World Health Organization and UNICEF.

The medical situation is under control in the flood zone, he said, despite some disease outbreaks, but the situation is still tenuous.

Flood survivors line up for food in a camp set up for displaced people in Nowshera, Pakistan, on Tuesday. (Mohammad Sajjad/Associated Press)

"Health problems usually arise in flood-affected areas after four to six weeks, and we need to be alert and prepared to tackle the situation," he said.

Prime Minister Yousuf Raza Gilani warned that the country has to prepare for epidemics.

"Pakistan and its people are experiencing the worst natural calamity of its history," Gilani said at a meeting on health issues in the flood zone. "As human misery continues to mount, we are seriously concerned with spread of epidemic diseases."

More than 3.5 million children are at risk from water-borne diseases, he said, and skin diseases, respiratory infections and malnutrition are spreading in flooded areas.

The problem is compounded by the flood's impact on the country's medical system, which is already badly overstretched and underfunded. Gilani said the floods had damaged more than 200 health facilities, for instance, and about one-third of the country's 100,000 female health workers have been displaced.

On Tuesday, officials announced that the government would give the equivalent of $230 US to every family affected by the floods, with a statement from Zardari's spokesman calling the payment "initial assistance."

In Shadad Kot, in the southern province of Sindh, authorities are increasingly worried that even the 18 kilometres of new levees that soldiers have built may not hold back floods in the city, and in Qambar city farther to the south.

On Tuesday, workers piled stones and sandbags to plug leaks in the levees, trying to stay ahead of any damage to the defences.

The flood waters, which have devastated lives from the mountainous north to the southern plains, are expected to begin draining into the Arabian Sea in the coming days.