May 27 (Bloomberg) -- More than 420,000 houses collapsed in Qingchuan County in southwest China after two aftershocks hit the region, already devastated by the country's deadliest earthquake in 32 years, state-run Xinhua News Agency said.

A magnitude-5.7 quake hit at 4:37 p.m. today in the region, the U.S. Geological Survey said on its Web site. A 5.2-magnitude aftershock hit about half an hour earlier, USGS said. Both occurred northeast of Wenchuan, the epicenter of the May 12 earthquake, with the larger quake centered 250 kilometers southwest of Xi'an, the home of the terracotta warriors.

A 6-magnitude quake in the area on May 25 left at least eight people dead, Xinhua said yesterday. The aftershocks are disrupting relief work and bringing more rubble down from mountains.

The new quakes came as Chinese troops prepared to blast barriers caused by the May 12 temblor to drain lakes that are threatening to burst and inundate towns trying to recover from the disaster.

About 600 military engineers and soldiers were working on the barrier that created the lake upstream from Beichuan in Sichuan province by 9 p.m. local time yesterday, Xinhua said, without saying when blasting would begin. Bulldozers and other digging equipment were flown in and officials are preparing to evacuate people.

``Around 100,000 would be evacuated to ensure their safety according to the current drainage plan,'' Liu Ning, the Ministry of Water Resources chief engineer, was cited as saying.

35 Lakes

The Tangjiashan lake is one of 35 caused by the earthquake on May 12 that killed 67,183 people and left 20,790 missing, according to figures released today by the government. The earthquake devastated highways and roads throughout mountainous eastern Sichuan, forcing soldiers and engineers to trek to areas such as Tangjiashan carrying dynamite and equipment.

The water level of Tangjiashan, the most dangerous of the quake lakes, rose 1.6 meters (5.2 feet) yesterday, Xinhua said.

The lake contains 130 million cubic meters (34 billion gallons) of water and is about 26 meters below the lowest part of the barrier, which was created when a part of a mountain collapsed into the Jianhe River. As many as 1.3 million people may have to be relocated if the quake lake is fully opened, Xinhua reported.

As many as 1,800 engineers, soldiers and policemen are being sent to the barrier. Soldiers are bringing in 10 kilograms (22 pounds) of dynamite each to move as much as 100,000 tons of debris and drain the lake, Xinhua said.

Engineers are also working to reinforce barriers downstream to prevent flooding when the water is released. About 687 kilometers of embankments throughout Sichuan need to be checked, Xinhua said.

Evacuation Plans

Evacuation plans have been prepared for communities near 19 lakes, E. Jingping, deputy minister of the Ministry of Water Resources, said May 25. Sixty-nine reservoirs were also in ``immediate'' danger of bursting and measures, such as draining the worst-damaged, are being taken.

Areas around the disaster zone may experience light rain through May 29, according to the China Meteorological Administration's forecast today. Sichuan's rainy season will start next month.

The 7.9-magnitude temblor two weeks ago injured 361,822 people, the State Council Information Office's spokesman, Guo Weimin, said today. Rescue workers pulled 6,541 people from the rubble, he said.

The quake affected more than 45.6 million people and about 15 million have been evacuated, Xinhua said today. More than 5.2 million people were made homeless, the government said earlier.

Tent Deliveries

The Ministry of Civil Affairs signed contracts with 75 enterprises to deliver 900,000 tents before June 20, it said in a statement. Almost 496,000 tents were delivered by yesterday, Xinhua said.

The government earlier called for 3.3 million tents and said it will build 1.5 million temporary houses for survivors.

Donations from abroad and at home amounted to 32.7 billion yuan ($4.7 billion), Guo said today.

More than 155 governments, non-government organizations and international bodies have pledged 1.9 billion yuan, Foreign Ministry spokesman Qin Gang said today at a regular press briefing in Beijing. Of that 668 million yuan has been received.

The May 12 earthquake was the most powerful to hit China, the world's most populous country, since a magnitude 8.6 quake struck Tibet in 1950, killing 1,526 people.

A 7.5 magnitude temblor in Tangshan in the northeast killed 250,000 in 1976, according to the USGS. China's seismology department said the Sichuan quake had a magnitude of 8.

To contact the reporters on this story: Dune Lawrence in Beijing at dlawrence6@bloomberg.net; Aaron Sheldrick in Tokyo at asheldrick@bloomberg.net.

Last Updated: May 27, 2008 10:44 EDT