China has said a massive lake formed by China's Sichuan earthquake is halfway drained and now poses less of a threat. China says it has won a decisive victory in its battle to drain the lake; drainage efforts began Saturday, Chinese troops were forced to use anti-tank weapons to blast away rocks to speed up drainage. Meanwhile, China has punished more officials for doing a poor job with earthquake relief work. Daniel Schearf reports from Beijing.

China's official Xinhua news agency reports the Tangjiashan quake lake has drained more than halfway, significantly easing the threat from flooding.

The unstable lake contained 250 million cubic meters of water and was formed when Sichuan's May 12 earthquake caused landslides to cut off a river.

Xinhua said there was now a balance between the inflow and outflow of water and that pressure on the lake's dam had eased.

More than 250,000 people had been evacuated from the area and more than one million others were directly under threat if the lake burst. But, Xinhua says only 50,000 people are still threatened.

Mao Qunan, a spokesman for the Ministry of Health's news department, says if the barrier lake breaks it will probably flood a big area, posing a severe challenge to epidemic prevention work in the disaster area.

Soldiers had worked for days digging a channel and blasting obstacles with dynamite and short-range missiles to ensure a fast flow of water.

The draining water flooded large parts of Beichuan, a town devastated by the earthquake and now abandoned.

Xinhua reported televisions, refrigerators, and corpses floating in the water.

China's public security chief, Zhou Yongkang, toured the earthquake zone after protests by parents over alleged shoddy school construction. Thousands of students died in the earthquake after their schools collapsed on them.

Chinese authorities have vowed to investigate all school construction and severely punish any wrong-doing.

Xinhua said 15 officials in Sichuan were fired for their slow response to the disaster or for mishandling relief work and another 13 were given administrative punishment. The report gave no further details.

Meanwhile, wreckage from a rescue helicopter that had crashed in late May was found. All five crew and the 14 quake victims they tried to save died in the crash.

More than 69,000 people were killed and nearly 18,000 are missing from the earthquake.