Hundreds of troops carrying explosives trekked through a quake-devastated area in southwest China on Sunday, attempting to reach a "quake lake" that threatens a secondary disaster. Concerned by a steep rise in the water level of a giant lake at Tangjiashan, authorities want to blast a hole in the barrier before it bursts and causes a flashflood. Thousands have been evacuated below the lake as a precaution. Also on Sunday, state television reported an 80-year-old partially paralysed man had been pulled alive from rubble, 266 hours after the 7.9 magnitude quake hit. The man was rescued on Friday in Mianzhu city, where he had been trapped under a collapsed pillar of his house. He had survived after being fed by his wife, the television report said. Premier Wen Jiabao, who believes the overall death toll from the May 12 earthquake could exceed 80,000, has said the main concerns are now secondary disasters like flooding and landslides, epidemics and providing shelter for nearly 5 million displaced. The biggest concern is the lake at Tangjiashan which rose 1.93 metres on Saturday to 723 metres, Xinhua said. State media reported that bad weather had prevented the airlift of personnel and equipment into the area, and that 1,800 soldiers were sent to the lake by foot. Each soldier was carrying 10 kg of explosives, Xinhua state news agency said. The lake is just 3.2 km upstream from Beichuan, a town so badly hit that it will be rebuilt in a new location and the ruins of collapsed buildings left as a quake memorial. Workers also plan to dig tunnels to drain water from dozens of other unstable lakes that built up after landslides blocked rivers in the Sichuan province. The government fears that as water levels rise they could burst, drowning survivors and rescue workers downstream. LANDSLIDES Troops said on Sunday that any controlled release of water would not present any danger for locals, but nonetheless farmers said they were worried. "At night-time you can hear the rumbling from the landslides around here and sometimes the earth shakes," said Yang Daifu, 70, a farmer from Nongwan village, which was nearly completely wiped out in the earthquake. "We see the water is rising as well, so we still feel threatened here," said Yang, who now lives in one of the tens of thousands of state-issued blue tents a few kilometres from his old home. Soldiers, relief workers and survivors are already pushing on with cleaning ruins and agricultural work, although mountainous terrain means some places are still cut off after highways buckled, bridges collapsed and landslides blocked roads. Before Friday's rescue in Mianzhu, the previous longest survivor had been a woman who was rescued after spending 196 hours under the rubble, according to state media. But almost two weeks after the quake, the chance of finding anyone else alive is tiny, although officials say they have not given up the search for survivors, especially a handful believed still trapped in coal mines. On Saturday, UN Secretary-General Ban Ki-moon made a one-day visit to the flattened town of Yingxiu, which lost an estimated two-thirds of its inhabitants in the 7.9 magnitude quake and has almost no safe buildings left standing. Ban, who flew to Asia to convince Myanmar to allow better aid flows into the cyclone-ravaged country, praised China's response to the quake. "The Chinese government, at the early stage of this natural disaster, has invested strenuous effort and demonstrated extraordinary leadership," he said. (US$1=6.941 Yuan) (Writing by Jeremy Laurence; Editing by Alex Richardson) Story by Chris Buckley REUTERS NEWS SERVICE