The onset of the rainy season threatens to swell dangerous "quake lakes" and compound the difficulties of reconstruction after China's worst earthquake in decades.
The 7.9 magnitude tremor and the thousands of aftershocks that followed have changed the landscape of the northern Sichuan province forever. Rivers were blocked, weakening mountain walls and creating unstable lakes where there was once dry land and more than five million buildings collapsed, according to an official.
The death toll has already passed 55,000, with almost 25,000 missing and more than 281,000 injured, Sichuan vice governor Li Chengyun said today as fears grew that disease, rain and aftershocks could bring yet more disaster to the southwestern province.
He said this was a "peak period for outbreaks of diseases", describing the situation as very grim, but was optimistic about short-term relief.
"We will strive to provide safe, economical and convenient temporary housing for 98 percent of the residents within the next month," Li told a Beijing news conference, adding that it would take three years to rebuild "new villages, towns and cities".
In Chengdu, some volunteer relief convoys reported being held up by hungry residents, one at gunpoint. There were reports of two people being beheaded by helicopter blades, one at the Wolong panda reserve, sources in Sichuan and local reporters said.
Premier Wen Jiabao, making his second visit to the disaster zone, visited hospitals and tents sheltering quake refugees today in Beichuan county, one of the worst-hit areas.
In a temporary shelter for the Beichuan Middle School, which lost up to 1,000 students and teachers in the quake, Wen tried to cheer up children, writing a line on the blackboard reading "Deep distress resurrects a nation".
Wen, a trained geologist, had earlier ordered rescue workers to eliminate the danger of the lakes "through engineering means" while swiftly evacuating people in their path.
In Hongguang, in northeastern Sichuan, the earthquake caused both sides of a valley to slide, burying three villages and 900 people. The Qingzhu River is trapped behind.
"The mountains merged," said Gao Xiao, who barely escaped a landslide that roared past her house.
The Qingzhu landslides have formed five lakes, the biggest of which is almost 30 metres (100 feet) deep. A flood control team monitors the natural dams constantly, for fear they will burst and unleash a wall of water on the valley below.
The more than 30 barrier lakes in the quake were safe for the moment and residents under threat had been evacuating, Zhu Bing, a Sichuan water resources official, told the news conference.
"There is a possibility of (the dam) collapsing entirely in the case of a strong aftershock or rainstorm," Zhu said of the Tangjiashan barrier lake in Beichuan which Wen toured on Thursday.
Heavy rain is forecast, making life even more difficult for rescuers, relief workers and the 5.48 million either living in tents or under makeshift cover as their mourn their dead.
Sichuan has been on high alert for epidemics, said vice governor Li. "The most-needed items remain tents and pre-fabricated housing units," he said. "We also need hygiene equipment such as street-cleaning and water-spraying vehicles."