An aftershock has rocked the earthquake zone in Sichuan province, shaking a huge lake formed by the quake nearly one month ago and threatening to engulf more than one million people downstream.
The earthquake, on 12 May, formed more than 30 "quake lakes" after landslides blocked rivers, raising fears that flooding could be the region's next biblical and epic disaster.
Aftershocks are still rocking Sichuan. The magnitude of yesterday's 20-second tremor was unknown, although the United States Geological Survey reported a 5.0 magnitude earthquake at the exact same time, with its epicentre located 70 kilometres north-west (44 miles) of earthquake-battered Mianyang.
Landslides, which were responsible for much of the earthquake damage in the worst-affected places such as Beichuan, have continued to plague the mountainous region, sending large boulders crashing down the slopes.
The largest lake is the Tangjiashan lake, where 220 million cubic metres of water behind the lake's natural mud-and-rock dam rose to 2,440 feet above sea level at one point, a perilous half-metre from the sluice, according to local reports.
It's a mammoth task for the soldiers of the People's Liberation Army, who are clambering around laden with dynamite or carrying handheld rocket launchers trying to blow up houses and large rocks to help speed the flow of water into a channel they started digging last week. Other troops were digging a second channel on the other side of the dam. However, the lake has continued to swell over the past few days in heavy rainfall.
More than 69,000 people have been confirmed dead in the quake so far, which has left at least five million people homeless. There are still 18,000 people missing.
Before the aftershock, the Xinhua news agency reported that drainage work had been going smoothly, but it also issued grim reminders of the effect that previous disastrous "quake lakes" had. A number of the lakes burst their banks weeks after powerful earthquakes hit the same area in 1786 and 1933, both killing several times more people than those who died directly from the tremors.
"Construction of the lake's drainage projects goes on well, but the lake remains dangerous for hundreds of thousands of people downstream," said General Ge Zhenfeng, supervising the relief work. "It will take us a few days to eliminate the potential danger."
About 1.3 million people live downriver of the lake and a quarter of a million people have already been evacuated from Beichuan, Mianyang and Jiangyou, adding to the millions already displaced.