UN Secretary General Ban Ki-moon has urged the world to speed up aid to Pakistan after devastating floods which the government says have affected 20 million people.
Mr Ban is in Pakistan to visit PM Yusuf Raza Gilani and President Asif Ali Zardari, whose handling of the crisis has been widely criticised.
The risk of epidemics in flood-hit areas is now seen as a serious threat.
On Saturday, the UN confirmed at least one case of cholera among the victims.
"I'm here also to urge the world community to speed up their assistance to the Pakistani people," Mr Ban told reporters as he arrived.
"We will try to mobilise all necessary assistance and remember that the whole world is behind the people of Pakistan in this time of trial," he said, adding he would report back to the UN General Assembly first thing this week.
Despite the scale of the disaster, Pakistani officials have expressed concern about the international community's response.
On Saturday, Pakistan's UN envoy Zamir Akram told the BBC that the immensity of the devastation was only now being recognised, and that so far there had not been enough help.
The UN on Wednesday launched a $459m (£294m) appeal for emergency aid, but says billions will be needed in the long term.
The US is at the forefront of the relief effort, having donated at least $70m to the country, which is a key regional ally in fighting terrorism.
The US has also sent military helicopters to rescue stranded people and deliver food and water.
Pakistan's government itself has been dogged by accusations that it has been slow to respond to the crisis, and Mr Zardari has been criticised for not cutting short a trip to Europe as the crisis unfolded.
Flood levels are expected to surge even higher along parts of the already dangerously swollen Indus river, with disaster officials saying "major peaks" were expected next week in Punjab and Sindh provinces.
On Saturday, Mr Gilani said 20 million people had been affected by the country's floods, a much higher estimate than the UN's 14 million.
"Unfortunately, the recent unprecedented torrential rains and devastating floods have made more than 20 million people homeless, destroyed standing crops and food... worth billions of dollars, washed away bridges, roads, communication and energy networks," he said.
There were still flood victims to be reached, but the government was leaving no stone unturned, he said.
The UN had previously said the region's worst flooding in 80 years had affected 14 million out of Pakistan's 180 million population and killed 1,600 people.