Hundreds of thousands of Pakistanis have fled floodwaters after the surging River Indus smashed through dykes in the southern province of Sindh.
About 175,000 people are believed to have fled their homes overnight in Thatta city after the rampart protecting the city was breached.
Authorities were trying to repair the dyke, about 75 miles south-east of the major port city of Karachi.
But a second breach occurred in the Soorjani dyke in the same region and local disaster official Hadi Baksh Kalhoro declared: "The situation is getting worse - the water is flowing into a nearby canal endangering Thatta."
Relief organiser Gulab Shah reported that thousands of people are "sitting with their cattle and belongings and their lives are in danger, but they are not willing to leave."
Residents who said that they heeded evacuation orders, but now had no food, water or shelter, blocked a nearby highway with burning tyres.
UN spokesman Maurizio Giuliano said: "We are delivering aid faster and faster, but the floods seemed determined to outrun our response."
On Thursday the Pakistani Taliban charged that the US and other Western donor countries were not really focused on providing aid.
A spokesman for the Islamist movement said: "Behind the scenes they have certain intentions, but on the face they are talking of relief and help.
"No relief is reaching the affected people, and when the victims are not receiving help, then this horde of foreigners is not acceptable to us at all."
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