UN chief Ban Ki-moon said Pakistan faces a "slow-motion tsunami" as the flood-ravaged nation stepped up pleas for massive global aid, warning that Islamist militants could exploit the crisis.
Ban told a UN emergency fundraising session in New York on Thursday that the world had a duty to act while millions are still without shelter and a fifth of the country -- roughly the size of England -- submerged by flood waters.
"It is one of the greatest tests of global solidarity," Ban told the General Assembly meeting, saying that Pakistan was facing a "slow-motion tsunami."
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Although weather forecasters say the monsoon systems are easing off and water levels receding, the fallout from three weeks of devastating floods that have left nearly 1,500 people dead is likely to last for years.
Pakistan and the United States have voiced growing fears that extremists may harness the discontent to further destabilise Pakistan's embattled government, or that unhappiness with relief efforts could fan social unrest.
"I stand before you as the voice of 20 million Pakistanis devastated by the floods," Foreign Minister Shah Mehmood Qureshi told the meeting in New York.
"The massive upheaval caused by the floods and the economic losses suffered by the millions of Pakistanis must be addressed urgently. We cannot allow this catastrophe to become an opportunity for the terrorists."
The nuclear-armed nation of 167 million is a top US foreign policy priority due to concerns over Islamist extremism.
Washington says its porous border with Afghanistan provides cover for militants to attack US-led troops fighting a nine-year insurgency there.
Nuclear-armed Pakistan is also locked in battle with homegrown Taliban who have been blamed over a three-year bombing campaign that has killed more than 3,570 people.
In a poignant video message to the meeting, US Secretary of State Hillary Clinton urged generosity, saying: "This is a defining moment -- not only for Pakistan, but for all of us."
Clinton raised US aid to 150 million dollars, while Britain said it planned to double its contribution to more than 99 million dollars.
Eight million flood survivors in desperate need of food, shelter and clean drinking water require humanitarian assistance to survive, as concerns grow over potential cholera, typhoid and hepatitis outbreaks.
In the southern province of Sindh, eight people, including four children, have died from skin and stomach diseases in the last three days, local government spokesman Jamil Soomro said Friday.
In central province Punjab, which together with Sindh are the most densely populated parts of Pakistan and the country's agricultural backbone, officials said water levels were going down and some key roads reopening.
Suhail Chaudhry, administration chief of the Layyah district, said people were returning to partially damaged homes. "We expect more will leave in large numbers over the next 2-3 days," he said.
The floods wiped out villages, farmland and infrastructure, and UN aid coordination body OCHA said more than 650,000 homeless families were still without basic shelter.
At camps for the displaced from across the country, survivors are battling with crippling heat, miserable sanitation and swarms of mosquitoes.
Many fled their homes with just the clothes on their backs and have been forced to drink contaminated water, causing diarrhoea and heightening fears over outbreaks of cholera and other water-borne diseases.
At a camp in Sukkur, Sindh province, women and children queued patiently for a cooked meal -- dished out from vats in the back of a truck -- while others waited for basic medical care at a makeshift clinic.
Qureshi put the economic damage of the floods at 43 million dollars and the Financial Times reported Friday that Pakistan would ask the International Monetary Fund to restructure a 10.5 billion dollar loan agreed in 2008.
Islamabad has concluded that it is now impossible for it to meet the conditions of the lending programme agreed in 2008, the paper quoted Pakistani officials as saying.
The Asian Development Bank has said it will give two billion dollars to repair roads, bridges, power lines, homes, schools, medical facilities and farm structures, and the World Bank has promised to lend 900 million dollars.
