Two Mi-17 helicopters carrying armed police and heavy-duty machinery left?Mianyang on Saturday despite bad weather and headed for a flood-prone quake lake at Tangjiashan Mountain.

Low visibility in the quake-stricken city in Sichuan Province has hindered airlifts to the lake, which is in danger of bursting.

The lake is one of several dozen that formed in the disaster region after quake debris blocked rivers.

Helicopters, including an Mi-26, the world's largest transport helicopter, have been poised at the Mianyang Nanjiao Airport since Friday, waiting to send about 350 armed police and 10 pieces of heavy equipment to the quake lake for emergency relief.

"Visibility in the past two days was below 1,200 meters, lower than the 2,000-meter minimum flight requirement for the Mi-26 and Mi-17 heavy transport helicopters," said Feng Jianhua, director of the civil aviation bureau in Mianyang.

He said that the weather began to clear on Saturday afternoon.

A smaller helicopter took five police to the site earlier on Saturday amid heavy fog for geological reconnaissance. That team also searched for routes for flood discharge channels, according to Zhang Maosheng, who took command of the flight operation.

As of Friday, the lake had collected about 100 million cubic meters of water and was in danger of overflowing, which posed a threat to residents downstream. The lake is 3.2 kilometers upstream from the Beichuan County seat, from which thousands of survivors have been evacuated.

Roads in the vicinity remain blocked, so the site must be approached by air. Feng said that the round-trip flight between Mianyang and Tangjiashan takes about 90 minutes.

Workers plan to dig channels to reduce the water level in the lake.

(Xinhua News Agency May 24, 2008)