BEIJING -- A huge volume of water Tuesday surged from a lake created by China's massive earthquake, safely plunging downstream through an area where hundreds of thousands had been braced for disaster, officials said.

The mammoth effort to drain Tangjiashan lake -- where floodwaters behind a landslide had threatened to burst through the wall of rubble to submerge low-lying towns -- was declared a success by officials who said the crisis was over.

But with the risk of man-made drainage channels collapsing under pressure from the water charging through them, there was still a danger of sudden tidal waves.

The official Xinhua news agency reported late Tuesday that a crest of flood water, carrying with it trees, TVs, refrigerators and the bodies of earthquake victims, had surged safely past the city of Mianyang in southwestern Sichuan province.

An engineer prepares to fire a missile to blast boulders in a man-made spillways in Tangjiashan, China.

Up to 250,000 people had already been evacuated from the area ahead of the deluge, but 400,000 remained in the city, where minor flooding and damage to buildings was reported as the torrent surged past.

The flood waters were released earlier by engineers and troops who had toiled for days using mechanical diggers, dynamite and anti-tank weapons to blast drainage channels through the landslide dam.

It was feared that a breach in the dam could threaten areas downstream that are home to more than 1.3 million people.

Meanwhile, officials found the crash site of a Chinese military helicopter that went down late last month in the mountains of southwestern China, killing 19 people, state-run media reported.

The transport was carrying a crew of five along with 14 injured residents from Sichuan province on May 31 when it crashed in "fog and turbulence" near Yingxiu in Wenchuan County, a military source told the Xinhua news agency.

The flight was a part of rescue efforts following the May 12 earthquake that devastated much of the region.

More than 69,000 people died in the May 12 quake, but more than 17,000 remain missing, according to the official government toll.