Pakistan said on Friday that 12 million people have been affected by floods that have destroyed hundreds of thousands of homes and claimed more than 1,600 lives, dpa reported
Nadeem Ahmed, head of the National Disaster Management Authority, said the the north-western province of Khyber-Pakhtunkhwa and central province of Punjab had suffered most.
Data was still being collected in the southern province of Sindh, where authorities were moving people to safer places as the rising Indus River threatened to submerge vast areas.
Ahmed said 650,000 houses were damaged or destroyed and the country would need 2.5 billion dollars for relief and rehabilitation after the worst floods in the country's history.
The deadly floods triggered by last week's unusually heavy monsoon rains devastated much of the north-western region, inundated hundreds of villages in central Pakistan and killed more than 1,600 people.
The raging waters have now poured into the 3,320-kilometre long Indus River and are passing through Sindh.
"At the moment 962,678 cubic feet (27,263 cubic metres) per second of water is passing through the Indus River in Sindh and its level is increasing," said Qamar-uz-Zaman Chaudhry, head of the Pakistan Meteorological Department.
Hundreds of troops and aid workers were strengthening river embankments and people were being evacuated from low-lying areas.
"Eleven districts are at risk of flooding in Sindh, where more than 500,000 people have been relocated to safer places and evacuation still continues," said a statement from the United Nation's humanitarian affairs body, UNOCHA.
The authorities set up relief camps in several official buildings but tens of thousands of people were staying in the open with their belongings, along roads or in fields, because of the lack of government-provided shelters.
In Punjab and Khyber-Pakhtukhwa, hundreds of thousands of people were still marooned by the floods, many of them forced to take shelter on rooftops and ridges.
Flooding submerged Jampur, a city of 200,000in the southern part of Punjab, forcing people to abandon the town abruptly, leaving behind their possessions. Hundreds more were stranded on rooftops.
Pakistani President Asif Ali Zardari has come under heavy criticism for visiting Europe while the country is reeling under the floods. This comes as his popularity nose-dived to 20 per cent, according to one poll.
His government is also facing the fury of the flood victims because of the slow pace of rescue and relief activities.
"There is no official, no government that has come for our rescue. Our houses, our belongings, our children have drowned in the flood and our president has no concern for us. We can only curse him and we are cursing him," said Allah Bux, a Jampur resident.
Many flooded areas remain inaccessible to relief workers and a new spell of rain that started on Friday in northern and north-western areas had hampered aid operations.
"This monsoon is quite intense. It will continue till August 15," said Arif Mehmood, chief meteorologist at the Pakistan Meteorological Department.
"The current spell will continue till Sunday and it can halt flight operations in the flood-affected areas and will create further difficulties in the areas where thousands of people have lost shelter," said Mehmood.
The World Health Organization (WHO) reported that cases of acute diarrhoea were a source of concern.
"There are random cases of acute diarrhoea in four of the most affected districts. But there is no outbreak of diarrhoea reported so far," said Haider Ali, a WHO official in Khyber-Pakhtunkhwa.
"But we are concerned. Dead animals are still in the water and the stink is spreading everywhere," he added.