The bustling construction site where China's fourth-largest airport is being built came to a sudden standstill yesterday, when the local government ordered all work suspended pending safety reviews following Sunday's bridge collapse that killed seven workers.

Rescuers use life detectors to search for survivors in debris of a collapsed overpass at the new Kunming Airport January 3, 2009. Seven people were killed Sunday after an overpass under construction collapsed in southwest China's Yunnan Province, local officials said.[Xinhua]

The accident, which took place near Kunming, capital of southwest China's Yunnan Province, also left 34 injured, eight seriously.

Exactly what caused a 38-meter section of an overpass under construction to plunge 7.5 meters to the ground is under investigation, said Wang Jinsheng, spokesman for the construction headquarters of the new airport, which is due to be completed by 2012.

But Wang dismissed speculation that the workers had rushed the construction work, giving safety and quality a backseat.

"They were not hurrying to finish the building of the overpass," said Wang speaking over the phone from the accident site.

But other voices told a different story. According to a Chongqing Evening News report today, a number of airport workers who were unwilling to reveal their names used the phrase "cheating on labor and materials" to describe the cause of the accident. A faulty steel frame was the main reason for the collapse, they said.

According to the workers, the horizontal support of the overpass steel frame should have been reinforced strictly in accordance with standards: all four sides should have been tightly fitted with connecting links every meter and the top and bottom parts should have been reinforced crosswise. A single unstable steel bar could cause the whole frame to collapse, they said.

The workers claimed that untrained women workers were recruited and participated in the building of the frame. They added that the project was sold and resold through multi-level contracting, reducing profit margins to the bare minimum. In order to break even, contractors cheated on labor and materials, including cutting down on steel reinforcements to increase "efficiency."

As a result, the steel frame looked normal but the inner section became loose. When tens of thousands of tons of concrete were added to the overpass, vibration transmitted by the machines caused the unstable frame to shake and collapse.

According to a spokesman for the Yunnan Construction Engineering Group, the main contractor for the airport construction, the results of the investigation might be available later today.

An estimated 20,000 workers were working on the construction site as of early December 2009, according to local media reports.

All those who died were migrant workers, five from Yunnan; one from bordering Guizhou Province and the other from northeast China.

The injured now are all out of danger.

The airport will become China's fourth-largest air transport hub after completion, targeting South Asian and Southeastern Asian countries, and will have an annual capacity of 38 million passengers and 950,000 metric tons of cargo by 2020.

More than 23 billion yuan (US$3.37 billion) will be invested in the airport, which covers 15.98 sq km.