Officials in Pakistan fear the flood crisis could worsen in the coming days if the already swollen Indus river bursts its banks.
Weeks of torrentials rain have been replaced by a spell of relative calm but already threatened areas remain in danger.
Local charities and international agencies have rushed food, water, shelter and medical treatment to the worst-hit areas in the northwest and Punjab and Sindh provinces.
But aid agencies and the British government have complained that the international response to the disaster has not been generous enough.
The World Bank said on Tuesday it will redirect $900 million of its existing loans to Pakistan to help in flood recovery, as the UN warned that many of the 20 million people affected by the disaster have yet to receive any emergency aid.
Pakistani President Asif Ali Zardari on Tuesday acknowledged that the government had responded poorly to the widespread flooding.
The floods have killed about 1,500 people and inundated 1.7 million acres of wheat, sugar cane and rice crops, raising the prospect of food shortages in the coming months in the already-poor nation.