LUDIAN, Yunnan, Aug. 6 -- Rescuers are continuing to comb through quake rubble in southwest China, after the expiry of the 72 hour "golden period" when finding survivors becomes much less likely.

Another 179 people were confirmed dead Wednesday, taking the death toll near to 600.

Most of the latest casualties were reported in Ludian and Qiaojia counties, where rescuers are concerned by the growing threat of barrier lakes, created when landslides block rivers.

QUAKE LAKE

Near the border of Ludian and Qiaojia, a barrier lake has led to the evacuation of 4,200 residents from the lower reaches of the Niulan River.

Sun Huaikun, who is in charge of the barrier lake response, said a reservoir on the upper reaches is intercepting river water to reduce pressure on the lake, while two hydropower stations on the lower reaches are speeding up the discharge of water from the lake.

Nine people in Qiaojia are missing, 2,400 are injured and another 230,000 have been relocated but are still suffering water and food shortages.

Over 280 km of water pipes and facilities at 37 water sources have been damaged or destroyed, cutting off supply to over 300,000 people. Local bottled water plants are providing 50,000 liters of drinking water every day, a woefully inadequate volume for the number of people in need. In relocation centers in worst hit areas such as Longtoushan, residents can drink bottled water and have hot meals.

Zhou Minghui, head of Ludian's water bureau, said an emergency water distribution network should have been ready by Wednesday.