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Chinese rescuers use shovels and heavy equipment to search for people buried by a landslide in Zhouqu County of Gannan Tibetan Autonomous Prefecture, Gansu province, on Monday. ((Aly Song/Reuters))

More than 6,000 troops sifted through mud-drenched villages and towns Monday in a desperate search for survivors of a series of flash floods and landslides in northwestern China.

At least 337 people were killed after the disaster struck China's Gansu province on Sunday, covering entire villages in water, mud and rocks. On Monday night the government said 1,148 were missing, down from a previous estimate of 1,300. About 45,000 were evacuated.

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Women mourn their missing relatives in Zhouqu County on Monday. ((Aly Song/Reuters))

Soldiers worked through the night heaving mud with bare hands and shovels, pulling mud-soaked corpses out of the rubble.

Debris also blocked the transport of much-needed bulldozers and backhoes from roads into the mountainous county seat of Zhouqu, which remained largely submerged following Sunday's disaster.

Work was underway to restore power, water and communications in affected areas in the southern part of the province, and it was not known how many of the missing were in danger or simply out of contact.

Hoping to prevent further disasters, demolition experts set off three sets of charges to clear debris blocking the Bailong River upstream from the ravaged Zhouqu.

The blockage had formed a three-kilometre-long artificial lake on the river that overflowed in the pre-dawn hours, sending deadly torrents crashing down onto the town. Houses were ripped from their foundations, apartment buildings shattered, and streets covered with a layer of mud and water more than a metre deep.

Premier visits area

Premier Wen Jiabao flew to the area on Sunday to oversee relief efforts and offer hope to those still trapped.

At one point, almost slipping in the brown muck surrounding him, Wen shouted encouragement to an elderly man trapped inside a collapsed house.

"Hang on, dear fellow! We're trying to save you!'" Wen was seen shouting, in Chinese, on state broadcaster CCTV.

Wen visited hard-hit areas including the Sanyan Valley, where a village of 300 households was buried in mudslides, the official Xinhua News Agency said. It said more than 680 villagers have been rescued, but gave no word on numbers believed to still be trapped.

Flooding in China has killed more than 1,100 people this year and caused tens of billions of dollars in damage across 28 provinces and regions.

There is more heavy rain forecast for the region over the next three days, the China Meteorological Administration said. On Monday evening, clouds were building ominously over the mountains where the mud first started flowing.

With files from the CBC's Anthony Germain and The Associated Press