Pakistan faces the risk of a public health disaster with up to 2.5 million people affected and 1,500 killed by devastating floods that have washed away entire villages, officials said.
The death toll was expected to rise on Tuesday in northwest Pakistan after the floods and landslides triggered by record rain last week obliterated homes and farmland in one of the country's most impoverished regions.
Aid officials said clean drinking water and sanitation were urgently needed to stop diseases such as cholera spreading among the survivors of Pakistan's worst floods in 80 years.
"Thousands of people are living in miserable conditions," Ateeb Siddiqui, director of operations with the Pakistan Red Crescent Society, said.
"Providing clean water and sanitation is an absolute priority if we are to avert a public health disaster," he said.
Flood victims have condemned authorities over sluggish relief, shouting "give us aid sent by foreign countries" and "death to the corrupt government".
At a camp set up by the army for around 640 families in the northwest area of Nowshehra, women and children ran after vehicles bringing food and water, pushing and shouting.
People at the camp said there were no proper toilets or bathrooms and that the only respite from the crushing heat was plastic hand fans. Most of them fled in the clothes they were wearing and many children roamed naked.
The United Nations said around 980,000 people had lost their homes or been temporarily displaced by the floods and the figure was likely to rise above a million.
An assessment by the UN World Food Programme in four districts -- Nowshera, Charsadda, Mardan and Peshawar -- found that around 80,000 homes had been destroyed and another 50,000 damaged.
Food, clean drinking water, tents and medical supplies were the most pressing needs, the UN said.
The International Committee of the Red Cross said that up to 2.5 million people across Pakistan had been affected by the flooding, with whole villages lost to the raging waters.
Aid workers and Pakistan's military conducted what relief efforts they could as officials warned that the death toll would rise still further.
Mian Iftikhar Hussain, the information minister for Khyber Pakhtunkhwa province, said Monday the toll from the floods stood at 1,200 to 1,500.
Provincial health minister Syed Zahir Ali Shah said about 100,000 people, mostly children, were suffering from illnesses such as gastroenteritis.
The province's chief minister Amir Haider Hoti said the floods were "unprecedented" and warned it could take up to 10 days to assess the overall number of dead and displaced.
Pakistan's meteorological service forecast rain of up to 200 millimetres (eight inches) in the next weeks across the northwest, Pakistani-administered Kashmir, the central province of Punjab and Sindh in the south.
UN chief Ban Ki-moon pledged aid of up to 10 million dollars for those affected by the crisis, while Britain pledged five million pounds (eight million dollars).
Helicopters sent by Washington have rescued more than 700 people from flood-hit areas, US officials said.
The National Disaster Management Authority said it had rescued more than 28,000 people in Khyber Pakhtunkhwa by helicopter and boat.
A spokesman for the charity World Vision said on Monday its teams had visited people affected around the main northwestern city of Peshawar, but that those further north remained stranded with roads cut off.
"They don't have drinking water or food. They said there have been some visible signs of water-borne diseases," spokesman Muhammad Ali said.