PM's call for help
Yousuf Raza Gilani, the Pakistani prime minister, visited flood-hit areas of Sindh province, calling again for international aid.
The disaster, he said, had spiralled beyond the government's capacity.
"Millions of people have suffered and still there is more rain and further losses are feared. I appeal to the world to help us, we are doing what we can," Gilani told reporters.
"The government has done everything possible but it is beyond our capacity, we are facing an extremely difficult situation."
He urged people threatened by the "unprecedented" floods to move to safer areas.
Those uprooted from their homes in Sindh have been moved to government buildings, schools and tents.
"I didn't want to leave but when the water levels got high and we were hungry and couldn't cook anything ... my brother told me we should leave," Najma Bibi said as she searched for food with her eight-year-old son.
Fresh downpours hammered the northwestern province of Khyber Pakhtunkhwa, with experts predicting at least another day of rain, adding to the misery of the millions made homeless.
Patrick Fuller, a spokesman for the International Federation of the Red Cross and Red Crescent, told Al Jazeera that his organisation is trying to reach those affected by the floods.
"People are camped out in the middle of the road under pieces of plastic," he said.
"The Red Crescent relief teams are on the ground but the scale of the problem facing us is absolutely massive.
"The numbers keep rising every day. This crisis just reels from bad to worse."
Floodwaters have roared down from as far away as Afghanistan and India through the northwest to the agricultural heartland of Punjab and on to southern Sindh along a trail more than 1,000km long.
Raging waters have spread for tens of kilometres from rivers, wiping out entire villages.
Meanwhile, Asif Ali Zardari, the Pakistani president, is preparing to return to the country after facing a barrage of criticism for going on a trip to Europe at the height of the disaster.
But Farhatullah Babar, Zardari's spokesman, told Al Jazeera there was "need for mobilising international support for the relief and rehabilitation of flood victims".
"This is precisely what Mr Zardari has been doing during his visit," he said.
"In all three countries he has received assurances and support for the relief and rehabilitation operation.
"The World Bank as well as the US announced support for Pakistan. So we believe it was important for the president to come out of the country."
The United Nations estimates at least 1,600 people have been killed by the floods that have ravaged the largely impoverished, insurgency-hit country, sweeping away entire villages.
Jean-Maurice Ripert, the UN special envoy to Pakistan, said "we are doing our best to assess the situation as it evolves very fast".
"We have sent assessment teams to as many places as possible, to be aware of the exact amount of assistance which would be needed for emergency relief," he told Al Jazeera.
"But beyond that one thing is certain: the extent of damages to the economy [and] infrastructure is enormous and will require a long-standing assistance from the international community ... The economic consequences of the floods will last for more months."
The flooding has threatened electricity generation plants, forcing units to shut down in a country already suffering a crippling energy crisis.
Some parts of the Punjab are under two metres of water, affecting nearly two million people, a senior crisis management official said, while in Pakistani-administered Kashmir 63 people have died and 1,000 families have been displaced.
"The scale of the needs is absolutely daunting," Melissa Fleming, a spokeswoman for the office of the UN High Commissioner for Refugees, said.
More than 252,000 homes are thought to have been damaged or destroyed across Pakistan and 558,000 hectares of farmland flooded, and it could be weeks before electricity is fully restored.
Pakistan's military said on Saturday it had rescued more than 100,000 people from flood-affected areas, while 568 army boats and 31 helicopters were being used for the rescue operation.
The army was also providing food and tents to the survivors, an army statement said.
But survivors have lashed out at the authorities for failing to come to their rescue and provide better relief, piling pressure on a cash-strapped administration struggling to contain Taliban violence and an economic crisis.