Emergency workers worked frantically to shore up a system of levees protecting two southern Pakistani cities from flood waters that have devastated wide swaths of the country, as a UN official warned that the crisis is "outrunning our relief efforts."
The floods, which began nearly a month ago with hammering rains in the country's north-west, have destroyed or damaged 1.2 million homes and affected 17.2 million people, UN spokesman Maurizio Giuliano said.
About 1,500 people have died in the floods, most in first few days, though the scale of the crisis - with immense social dislocation and agricultural destruction - continues to grow.
"The floods are outrunning our relief efforts. We move faster and faster, but the finish line keeps moving further ahead," Mr Giuliano said. "This is turning out to be a marathon, not a sprint."
While the flood waters are slowly moving toward the Arabian Sea, where they can drain away, the rainfall has been so intense that enormous parts of the country remain submerged.
In Shadad Kot, in the southern province of Sindh, authorities are increasingly worried that even the 10 miles of new levees soldiers have built to protect the city, and Qambar city further to the south, may not hold back the massive floods.
Workers were piling stones and sandbags to plug leaks in the levees, trying to stay ahead of any damage to the defences.
"It is the last-ditch effort to save the city," said Brig Khawar Baig. "We are trying to block the water here. If it crosses over, we fear it will go further south and inundate more towns."
Ninety percent of Shadad Kot's 350,000 residents have already fled the city. Many have also left Qambar and other nearby towns.
Water levels were still rising, Brig Khawar Baig said, but it was unclear when it would reach its crest.