UN Secretary General Ban Ki-moon has warned that Pakistan faces a 'slow-motion tsunami' as the flood-ravaged nation pleads for a massive injection of global aid.
Mr Ban told a UN emergency fundraising session in New York that the world had a duty to act with millions still without shelter and a fifth of the country submerged by flood waters.
'It is one of the greatest tests of global solidarity,' Mr Ban told the General Assembly meeting.
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.
There are growing fears that extremists may harness the discontent to further destabilise Pakistan's government.
'I stand before you as the voice of 20m Pakistanis devastated by the floods,' Pakistani Foreign Minister Shah Mehmood Qureshi told the meeting.
'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.'
In a 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.'
Mrs Clinton doubled US aid from $90m to $150m, while Britain said it planned to double its contribution to more than £64m.
At least 6m flood survivors in desperate need of food, shelter and clean drinking water require humanitarian assistance to survive, as concern grows over potential cholera, typhoid and hepatitis outbreaks.
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.
