The UN in Pakistan has described the humanitarian situation caused by the flood disaster as critical.
As floodwaters continue to travel south through the country, tens of thousands of people are being displaced each day.
Earlier, the UN said it had raised some 70% of the money needed to provide emergency relief to flood victims.
The International Monetary Fund is to start talks with Pakistan later to discuss what it can do to help deal with the crisis.
The IMF says the floods pose a "massive economic challenge" and it will review the country's budget and financial prospects.
The UN now estimates that the number of people who need basic shelter has gone from two million to six million.
Nearly 17 million people have been affected by the floods.
This week marks a month since the flooding started, and the United Nations says that, although it has raised close to 70% of the $460m (£295m) needed to provide emergency relief, many people have yet to receive any help, says the BBC's Jill McGivering in Sindh, the country's worst affected province.
Some $54m are in uncommitted pledges, and $263m are resources available now.
In the UK, relief agencies have said public donors have given £29m ($45m) to the relief effort.
They also said the international response had been slow to build up, but that they had received more donations in the second week than the first week, which was rarely seen in such appeals.
Tens of thousands of people have fled a threatened flood surge, with the south now bearing the brunt.
The water there has levelled out on the embankments around Shahdadkot, and is no longer a threat to the city, but nearly 80% of the population has already fled fearing the deluge, says the BBC's Shoaib Hasan in Islamabad.
The threat appears to have receded from the city of Hyderabad, where the flood control barriers have held against what local officials said was a "super flood".
Evacuation activities, meanwhile, have started in the Thatta district next to the Arabian Sea.
Dozens more villages have been inundated and although authorities expect flood waters to drain into the Arabian Sea over the next few days, evacuees who return may find their homes and livelihoods have been washed away.
An estimated four million people have now been displaced in the city of Sukkur alone.
Pakistan Prime Minister Yousuf Raza Gilani is to fly on Monday to the Gilgit Baltistan region in north-eastern Pakistan, where thousands of people are still trapped in areas cut off from each other.
The region as a whole remains cut off due to the closure of the Karakoram highway, its only road link to the outside world.
Sindh, in the south of Pakistan, is now being described as the country's worst-hit province, with officials saying at least 200,000 residents have fled in the last 24 hours.
The Pakistan government has said that the cost of rebuilding after the floods could be as high as $15bn (£10bn).
Overall, about 1,600 people have been killed and some 16.8 million affected, according to figures from the UN and Pakistani government.