Authorities in southern Pakistan are battling to save the town of Thatta, where the raging Indus River has breached more of its levees.
Tens of thousands of people have fled the town in the past few days and some outlying districts are reported to already be underwater.
The town, in Sindh province, is now all but abandoned, according to reports received by the BBC. A local official in Thatta says it could take up to three days to repair the breaches; but even if they can be repaired, thousands have no homes to return to.
The massive floods in Pakistan have lasted for more than a month, leaving eight million people in need of emergency relief.
As the waters start to recede in the north of the country, the full extent of the damage has begun to emerge.
Oxfam sounds dire warning
The international aid agency Oxfam says Pakistan will face devastating problems in the future unless flood reconstruction efforts begin immediately.
Oxfam says long-term relief work should be well under way by now, but says it has barely begun because the priorities are still providing people with shelter, clean water and sanitation.