Aid agencies in Pakistan have warned that many more people will die as floods inundate southern areas unless more international help comes.
The United Nations launched a fresh $459m appeal on Wednesday to help 14 million people affected by the deluge.
It says that so far about 1,600 people have been killed.
The UK charity, Oxfam, has described the floods as a "mega disaster" which require a "mega response". It says that so far that has not been forthcoming.
The UN's Food and Agriculture Organization (FAO) on Wednesday warned of serious threats to the livelihoods and food security of millions.
It says the devastation left by flood waters in the north and centre of the country may worsen as they continue to head south.
"One hundred percent crop losses have been recorded in many areas and tens of thousands of animals have been killed," it said in a statement.
"Nearly 700,000 hectares of standing crops are under water or destroyed and in many cases surviving animals are without feed.
"The upcoming fall [autumn] season's wheat crop is now at risk in a region that is the bread basket of the country."
The FAO says food prices have already started to rise sharply, at a time when more than 75% of the affected population depends on agriculture for their livelihoods.
The BBC's Aleem Maqbool in Islamabad says new areas in the south are being inundated by the hour.
Our correspondent says huge volumes of water that fell in the north several days ago still have not reached the sea - and scenes of villagers running from their homes carrying everything they own or being trapped on their roofs are being played out all the time.
The United Nations appealed on Wednesday for $459m to provide immediate help to flood victims.
UN Emergency Relief Co-ordinator, John Holmes, told the BBC: "Our immediate focus will be on the immediate humanitarian relief needs to actually keep people alive, to give them the basic minimum to stay alive, to survive."
Oxfam said that so far the provision of funds had been slow compared with the response to other recent humanitarian crises.
It said the international community had actually committed funding that works out at just over $3 per flood-affected person.
The commitment per person after the 2005 Pakistan earthquake was $70 and for this year's Haiti earthquake it was $495.
Meanwhile, the Pakistani Taliban and the banned Islamic charity Jamaat-ud-Dawa have called on the government to reject Western aid.
It says the money will only be siphoned off by corrupt officials.
Floods triggered by unusually heavy monsoon rains continue to leave a trail of destruction through the country.
Areas around Guddu and Sukkur Barrages in Sindh province remain in the "high flood risk" category.
Tens of thousands of people displaced from inundated villages are flocking to Sukkur city, which itself is under threat from rising water levels.
The Flood Warning Centre has predicted that a big wave will hit Sindh's Kotri Barrage, the last barrage on the Indus river, in the next 24 to 48 hours, threatening Hyderabad city.
In other developments:
- Fresh floods in Punjab province - upstream of Guddu - caused hundreds of thousands of people to move to safer areas, in many cases for the second time in as many weeks.
- Muzaffargarh, a Punjab city of 700,000 people, has been evacuated.
- In Balochistan province, officials say rains and floods have killed at least six people in Ziarat, Harnai and Loralai areas. Officials say that hundreds of people in these areas are trapped.
- Deaths have been reported in the Diamer area of Gilgit-Baltistan region.
- Pakistani and US helicopters are running sorties as part of a rescue and relief effort in northern parts of Khyber Pakhtunkhwa province.
Weather officials say the monsoon system over Arabian Sea is weakening.
They are forecasting a break in torrential rains for at least the next three days, though scattered rains are predicted in the north as well as the south.
Enraged survivors have been physically attacking government officials in flood-hit areas, amid widespread anger at the pace of the relief effort.
BBC Urdu will transmit six daily bulletins in Urdu and Pashto providing vital information including how to stay safe, avoid disease and access aid. Special programmes will be broadcast each day in Urdu at 12.30, 15.30 and 18.30 and in Pashto at 12.45, 15.45 and 18.45 (local times).