Floods triggered by exceptionally heavy monsoon rains in the northwestern province of Khyber-Pakhtunkhwa in Pakistan have killed at least 800 people and affected up to a million across the country.
Officials fear the worst is to come if floods hit the more populated provinces of Sindh and Punjab over the coming days, reports the United Nations.
The US government pledged an immediate $10 million in emergency aid, and relief and development NGOs are swinging into immediate action - although efforts are being hampered by difficult conditions.
"Dozens of homes here have been very badly damaged by water racing down from the hills and pouring into homes. People have been clinging to rooftops to try and stay safe," Inayat Jan, a local resident from a village in the Shangla district of Khyber-Pakhtunkhwa, told the UN Office for the Coordination of Humanitarian Affairs - Integrated Regional Information Networks (IRIN) over the phone.
In Khyber-Pakhtunkhwa, Swat, Dera Ismail Khan and Charsadda districts are the worst affected by floods.
"Flash floods triggered by the rains have also hit the seven tribal agencies located on the Pak-Afghan border," Basheer Bilour, Senior Minister for Local Government and Rural Development in Khyber-Pakhtunkhwa, told IRIN.
"There has been widespread destruction of crops while communities have been left stranded as water rises around villages and road links are cut," he added
The UN Office for the Coordination of Humanitarian Affairs (OCHA) said in a 29 July report that 25 districts in Khyber-Pakhtunkhwa had been hit by flooding, affecting at least 400,000 people. It said these were the worst floods in the region since 1929.
"Reports indicate that in Charsadda, more than 5,000 homes are underwater and 20 villages have been affected. The road links to Peshawar have also been cut off. In Swat, the Swat River has broken its banks. It is reported, four subdivisions have been affected, with two villages flooded and more than 1,000 homes underwater," said the OCHA report.
The government declared a state of emergency after the meteorological department said an "unprecedented" 312mm of rain had fallen in 36 hours in northwestern areas. It predicted "scattered showers" over the next few days in Khyber-Pakhtunkhwa, but warned of further rain in the eastern province of Punjab and in the southern province of Sindh.
OCHA said that while Khyber-Pakhtunkhwa was the worst-hit, more than a million people around the country had been affected by flooding.
According to media reports, at least 60 people were killed in floods in the southwestern province of Balochistan and humanitarian agencies say 150,000 people are affected there. Flooding has disrupted life in Upper Punjab, Gilgit-Baltistan on the Afghan border and Pakistan-administered Kashmir, where the BBC reported 22 deaths.
Some media reports put the countrywide death toll at around 1,300.
Relief efforts have been hampered by poor conditions and the fact that roads and bridges have been cut off by flooding.
"There is much havoc as around 50 bridges have been swept away," said Bilour.
OCHA said search and rescue operations were the most urgent and imminent need. "In addition, requests were also made for boats to facilitate access, rescue and assessment efforts. In terms of relief assistance, the authorities at provincial as well as national level requested support in emergency shelter, food (mainly ready-to-eat-food), health and sanitation."
National Disaster Management Authority (NDMA) chair General Nadeem Ahmed, speaking to the media in Islamabad, said that 17 helicopters were participating in relief efforts and that 900 people stranded in various locations had been airlifted to safe places.
With limited access to cut-off communities, aid workers are concerned that water-borne diseases could spread quickly.
"We must prevent disease. There are already reports of stomach problems among children," Dr Mahmood Khan, a physician working with Khyber-Pakhtunkhwa government teams in Peshawar and Nowshera, said.
Local resident Nazeer Ahmed, aged 40, from Mingora in Swat, said the flooding came at a time when people in the area had just begun rebuilding their lives after months of having been displaced by conflict between the army and militants.
"We are just recovering from months of conflict. The floods have in many cases affected farmers who were just rebuilding their lives and had only recently restored lands. Now, they have lost everything again," he explained. "We have very few medicines here and that is a problem, given that there is a danger of disease in many areas."
In Peshawar, about 70 families have taken refuge at a government school after water inundated their homes. "We were unable to remove our belongings or even documents; we just fled as fast as we could," Sameera Bibi told IRIN. Makeshift camps for displaced people have been set up in Swat and in the Peshawar and Nowshera areas.
With acknowledgements to UNIRIN