Hundreds of thousands of people who have been displaced are living in the open, exposing them to the diseases spread in the stagnant waters. They are in dire need of food, shelter, clean drinking water, toilets and medicines, authorities have said.
UNICEF has termed the situation of the families "beyond bleak".
It says an estimated 16 million children have been impacted, and at least 3.4 million girls and boys remain in need of immediate, lifesaving support.
The country received 391 mm (15.4 inches) of rain, or some 190% more than the 30-year average through July and August, a monsoon spell that started early and stretched beyond the usual timeline.
Rainfall in the southern province of Sindh shot up to 466% of the average.
The death toll from the deluge itself has touched 1,559, including 551 children and 318 women, which does not include the disease deaths, the country's disaster management agency said.
