Pakistan will need billions of dollars to recover from its worst floods in history, further straining a country already dependent on foreign aid to prop up its economy and back its war against Islamist militants, the UN says.



The warning on Sunday (Monday NZ time) came as officials said at least 53 people were killed in landslides in northern Pakistan and authorities rushed to evacuate thousands of people threatened by flooding that submerged villages in the south. The new devastation added to the disaster that has affected an estimated 15 million people.



The government has struggled to cope with the scale of the disaster, which has killed at least 1500 people, prompting the international community to help by donating tens of millions of dollars and providing relief supplies.



But the UN special envoy for the disaster, Jean-Maurice Ripert, said the need for foreign aid would be much greater going forward and could be difficult to procure given the ongoing financial crisis around the world.



The UN is still calculating specific figures, but Ripert said in an interview with The Associated Press that "the emergency phase will require hundreds of millions of dollars and the recovery and reconstruction part will require billions of dollars."



Much of that money will be needed in the northwest province of Khyber Pakhtunkhwa, the site of the worst damage from floods that first hit two weeks ago after extremely heavy monsoon rains. But as the floodwaters rushed south, they also brought death and destruction to the central and southern provinces of Punjab and Sindh.



The Indus river overflowed its banks near the city of Sukkur in Sindh on Sunday, submerging the village of Mor Khan Jatoi with chest-high water and destroying many of its 1500 mud houses, said Dadal Morai, a villager who lost his home.



Many flood victims have complained that they have not received aid quickly enough or at all, further undermining support for a government that was already unpopular.



"We are sitting on the bank with nothing in our hands; no shelter, no food," said another flood victim in Sukkur, Allah Bux. "We are helpless and in pain."



Thousands of other villagers in Sindh sought to escape the same fate by fleeing by donkey cart or on foot with their cattle and possessions in tow.



Late on Sunday, a magnitude-3.8 earthquake jolted Sindh, but no damage was reported, said Qamaruz Zaman Chaudhry, Pakistan's top meteorological official.



In Pakistan's far north, landslides triggered by heavy rains killed at least 53 people in two villages in the Gilgit-Baltistan area, senior government official Ali Mohamamd Sikandar said Sunday.



The landslides Saturday killed 37 people in the village of Kumra and 16 in Ghanche, he said. All the bodies in Ghanche have been recovered. Only 12 bodies have been found in Kumra, but the other 25 who are missing are presumed dead.