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Heavy rains lashed a remote section of northwestern China as the death toll from weekend flooding that triggered massive landslides jumped to 1,117, although the fading hopes of rescuers got a boost late Wednesday when a survivor was found in the debris.

The state-run Xinhua News Agency gave no immediate details on the survivor, found nearly four days after the disaster struck. Earlier Wednesday, a 50-year-old man was rescued after being trapped in knee-deep mud on the second floor of a hotel, Xinhua said.

Local officials have said at least 627 people are still missing.

The National Meteorological Centre warned there was a "relatively large" chance of more landslides in the coming days, as heavier rain was expected, with up to 90 millimetres forecast for Friday.

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Rescuers prepare to disinfect a landslide-hit street in Zhouqu County, China, on Wednesday. ((Aly Song/Reuters))

Troops and rescue teams, along with traumatized survivors, turned to recovering bodies and seeing to the needs of the living.

For crews working to stave off outbreaks of disease, clean drinking water was a primary concern. Most local sources of clean water have been destroyed or remain too polluted to use.

Entire communities in Gansu province's Zhouqu district were swallowed up when the debris-choked Bailong River jumped its banks Sunday, releasing wave after wave of mud and rubble-strewn water.

While torrential rains were the direct cause, tree cutting that left the dry hills exposed and the weakening of cliff faces by a massive 2008 earthquake were seen as contributing factors.

Buildings were torn from their foundations, their lower floors blown out by the force of the debris-laden water. Three villages comprising hundreds of households were buried entirely and much of the county seat left submerged.

Crews rushed Wednesday to drain an unstable lake on the Bailong upriver of Zhouqu with explosives and excavators, fearing more rain could cause another massive breach.

Families mourn

As the smell of death hung heavily in the air, disinfectant crews in protective suits sprayed chemicals across the ground and over machinery.

State media reported numerous cases of dysentery. Infected injuries, a lack of sanitation, clean drinking water and accumulating garbage also increased the risk of typhoid, cholera and other diseases.

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A girl stands on the debris of damaged buildings in Zhouqu County on Tuesday. ((Reuters))

Heavy equipment has been unable to traverse the difficult terrain or is mired in mud up to several metres deep, forcing rescue crews to rely largely on hand tools.

But roads reopened Wednesday, allowing heavy earth-moving equipment and supplies to flow in.

At least 45,000 people have been evacuated from their homes, and the Civil Affairs Ministry reported the delivery of 7,000 tents and 21,400 blankets to the area, with thousands more on the way. Zhouqu has a population of 134,000, but it wasn't clear how many needed emergency shelter.

Shen Si, a member of the Tibetan ethnic group native to the area, watched forlornly as troops dug to reach the bodies of her relatives inside their buried home.

"My mother and father in their 60s and my younger brother, all three of them, are buried here in our house still," she said.   

Throughout the area, bodies were seen wrapped in blankets and tied to sticks or placed on planks and left on the shattered streets for pickup.

Flooding in China has killed about 1,800 people this year and caused tens of billions of dollars in damage across 28 provinces and regions.