More than 175,000 people have fled Pakistan's southern city of Thatta, leaving it virtually empty, as flood waters threatened to submerge the city's outskirts.
Troops and civilians were struggling on Sunday to protect the city after floodwaters broke through levees on the Indus.
"The water is still two kilometres away from Thatta where the armed forces and the local administrative workers are working on war footing to save the city," Hadi Bakhsh Kalhoro, a senior city official told the AFP news agency.
"The army brought a maximum of resources to try to fill up the breach. Almost all the people have left Thatta to safer places, all shops and schools are closed," he said.
Thousands of people sought shelter on the high ground of a historic cemetery outside Thatta and others headed to nearby towns and cities.
Many were angered by lack of help, and on Saturday, a number of villagers blocked the main road in protest against the government, saying they had not received any food or assistance.
Lakano Barani, a resident from Thatta, blamed officials for not taking the necessary steps to prevent the third levee from breaking.
"Nothing was done and now it is too late. If they [the government] had taken action, then the historic city of Thatta could have been saved," he told Al Jazeera.
"The government has not told the people where to go or what to do. It is the most incapable government I have ever seen."
About 17 million people have been significantly affected by the floods and about 1.2 million homes have been destroyed or badly damaged, according to the United Nations.
More than 1,500 people have been killed.
The UN, the Pakistani army and a host of local and international relief groups have been rushing aid workers, medicine, food and water to the affected regions, but are unable to reach many people.
More than eight million people are in need of emergency assistance across the country.
"We are very concerned that, with more recent flooding in the south and nearly a million displaced in recent days, the challenges that are already there are continuing to grow," Stacey Winston, spokesperson for the UN Office for the Coordination of Humanitarian Affairs (OCHA), told Al Jazeera.
"More aid and funding is coming in, but we still need more. There is more flooding, more misery and more challenges. We are trying, as fast as we can, to reach as many as we can," she said.
Disease and hunger
The UN said that aid workers were becoming increasingly worried about disease and hunger, especially among children in areas where even before the disaster, acute malnutrition was high.
"We fear the deadly synergy of waterborne diseases, including diarrhoea, dehydration and malnutrition," Karen Allen, a senior Unicef official, said.
|The flooding, indicated in yellow, is expected to spread south with the Indus River [Al Jazeera]
Martin Mogwanja, the UN humanitarian co-ordinator, said the international response to the disaster must be more assertive.
"If nothing is done, an estimated 72,000 children, currently affected by severe malnutrition in the flood-affected areas, are at high risk of death," he said.
In Islamabad Phoebe Greenwood, from the international children's charity Save the Children, told Al Jazeera: "We have acute malnutrition here, which is when in a disaster children and families are not getting enough food at all. This has long-term implications for their health.
"There is an immediate need to get normalcy back into these children’s life."
Greenwood said that it would be important to set up temporary schools across the affected areas of Pakistan in order that children will be able to interact with each other although more funding was needed.
Meanwhile, the aid effort is gathering pace. Almost $700 million has now been donated to the flood appeal, both directly and through the UN.
The United States is taking the lead - contributing more than $100 million to the relief effort, while Saudi Arabia has handed over $34 million and the UK has donated more than $20 million.