CHENGDU, China A powerful aftershock destroyed tens of thousands of homes in central China on Sunday, killing at least six people and straining recovery efforts from the country's worst earthquake in three decades. More than 500 others were injured.
Meanwhile, soldiers rushed with explosives to unblock a debris-clogged river threatening to flood homeless quake survivors.
The fresh devastation came after a magnitude 6.0 aftershock among the most powerful recorded since the initial May 12 quake, according to the U.S. Geological Survey. The China National Seismic Network said the aftershock was the strongest of dozens in the nearly two weeks after the disaster.
The new tremor killed two people in Sichuan province and injured more than 480 others, 41 seriously, the official Xinhua News Agency said.
The news agency said today that the aftershock also killed four people and injured 20 others seriously in neighboring Shaanxi province.
Some 71,000 homes that had survived the original quake were leveled, and another 200,000 were in danger of collapse from the aftershock that caused office towers to sway in Beijing, 800 miles away.
Xinhua did not give any details on whether the houses were occupied.
Before the aftershock, the Cabinet said the confirmed death toll from the disaster had risen to 62,664, with another 23,775 people missing. Premier Wen Jiabao has warned the number of dead could surpass 80,000.
A mudslide caused by the aftershock blocked a road, but Xinhua said no serious landslides were reported.
Previous landslides loosened by the quake jammed rivers across the disaster area, creating 35 new lakes that placed 700,000 survivors in jeopardy of floods, Vice Minister of Water Resources E Jingping told reporters in Beijing.
The biggest concern was the new Tangjiashan lake in Beichuan county, where some 1,800 police and soldiers hiked with 22 pounds of explosives each to blast through debris, according to Xinhua.
The news agency said the soldiers arrived at the lake early Monday "and immediately began work to defuse the danger of a major flooding."
Hazy weather prevented helicopter flights to the area, and forecasts for rain increased the risk that lakes could overflow.
Rain will "not only cause the amount of water going into the lakes to increase but also influence their normal structure, so the situation is quite serious," said Vice Minister E. "It is a daunting task because of the unpredictability of when the barrier lakes will burst."
About 20,000 people have been evacuated from the disaster area due to the flood risk, and the total relocated could rise to 100,000, said Liu Ning, chief engineer at the Ministry of Water Resources.
The ministry also said 69 dams in Sichuan were in danger of collapse from quake damage, but reservoirs have been drained to lessen the risk. Authorities have said the world's largest water project the Three Gorges dam, located about 350 miles east of the epicenter was not damaged.
Elsewhere in the disaster zone, people ventured cautiously back to homes to retrieve belongings, but some decided the risk of entering damaged buildings was too great.
In Hanwang, 58-year-old Zhang Heqing was carrying a handful of plastic bags and had planned to go into his apartment block, but the coal mine employee said he had second thoughts.
"I just don't dare to go in," he said. "I live on the fifth floor and the staircase is blocked and you can't even open the doors."
Down the street, retiree Huang Huimei, 75, and her husband were busy stacking pots, pans, chairs and bed boards in a pile for movers to take to the provincial capital of Chengdu, where her son lives. Her building remained standing but had serious cracks and was not safe for habitation.
She had spent most of the time since the quake caring for her 95-year-old mother.
"I don't know if we'll be back," she said as her husband handed her part of a cooking stove through the front window of their ground floor apartment. "These apartments weren't that safe before the quake. My husband worked for the coal mine and it's supposed to rebuild the company apartments. But who knows when."
More than 15 million homes were destroyed in the disaster, and the Chinese government has appealed for tents to help shelter survivors.
Across town, about 10 families were living in makeshift shelters of picnic table umbrellas and nylon tarps draped over simple wood frames, pitched in a muddy lot that used to be a food market.
Chickens pecked at watermelon rinds, while the survivors used plastic basins to wash and piles of scrap wood for cooking fires.
"The local government officials have done a good job for themselves. They're living up there," said a camp resident who pointed to a neat row of tents up a hill.
"They didn't do such a good job here where the regular folks have to live," said the man, who would only give his surname, Wang.
State television reported Sunday that a survivor trapped by the initial quake was rescued alive Friday, more than 11 days after the disaster.
Xiao Zhihu, an 80-year-old bedridden man, was found in Mianzhu north of Chengdu, the report said. He survived because his wife was able to get food to him through the rubble of his collapsed house, but there were no further details given or a reason for the two-day delay in reporting the rescue.
Meanwhile, one of two pandas missing since the quake from a major preserve for the endangered animals in Wolong, near the epicenter, was sighted Sunday, Xinhua said. The panda, named Xixi, disappeared before staff could reach it, but was believed safe, the report said. The search will continue Monday.
The pandas' home at the world-famous Wolong reserve was badly damaged in the quake and five staff members were killed.
Contributing: William Foreman and Henry Sanderson