More than 1,500 people have been killed in the disaster over the past three weeks.
The United States, the U.N. and international relief agencies are scrambling to provide food and relief supplies to the affected areas.
But their efforts are being hampered by washed-out bridges and roads, as well as downed communications lines.
The floods have even washed away a three-month supply of relief items from the United Nations' UNICEF warehouse.
Waterborne illness is expected to quickly spread since many of the wells have been contaminated and dead animals are decomposing in the inundations.
Pakistan is likely to suffer acute food shortages for months if crops in the country’s breadbasket downstream from the flood zone become submerged.