A nearly completed 13-storey building in a middle-class neighbourhood of Shanghai collapsed yesterday, killing at least one person. Shocked homebuyers due to move into adjoining blocks demanded their money back. 'It's unbelievable and terrible. I am very worried about the quality of my flat,' one owner told Hong Kong's Cable TV. 'I definitely won't dare move into the building.' The block of flats in the city's southwestern district of Minhang keeled over at about 5.30am. Six decorators were working in the building when the accident occurred. One of them Xiao Xiao, a 27-year-old, was killed. 'At the beginning, the building leaned southwards and then collapsed entirely within half a minute,' a witness told the Shanghai-based Xinmin Evening News. 'Workers rushed out desperately.' Pictures showed the building tipped over at its base, exposing broken concrete pilings about 5 metres long. More than 100 families in the neighbourhood were evacuated to a school. Construction and decorators in other buildings in the same estate stopped work. The housing estate has been developed by Shanghai Meidu Property Company. It had sold 489 of 629 flats in the building. The average price of the flats was 14,300 yuan (HK$16,200) per square metre, and the estate was to open next May. Meidu could not be reached for comment. Dozens of people who have bought flats in the estate gathered in the area. Many were worried about the quality of other buildings and wanted their money back. Du Yueping, a Shanghai lawyer, said people who bought flats in the collapsed building could demand compensation. A section of a flood wall on the Puding River 20 to 30 metres from the building buckled on Friday, local media reported. The wall was pushed out several metres towards the river. Greg Wong Chak-yan, former president of the Hong Kong Institution of Engineers, said the problem with the flood wall could be one of the reasons the building fell. 'A lot of water flooded into the basement of the building after the wall buckled because it was the closest building,' Dr Wong said. 'The water caused great pressure to the base and the whole building fell back.' Mainland builders use prestressed, precast concrete piles, and Dr Wong said this could be another reason for the accident. 'The pilings were banned in Hong Kong because they are hollow and not strong enough to support high buildings of dozens of storeys like in our city. But they are commonly used on the mainland because their buildings are much lower.' Shanghai formed a team of construction, safety-supervision, transport and public-security officials after Mayor Han Zheng called for an investigation. The mainland's construction boom has led to poor building quality due to corruption and lax regulations. 'Tofu', or shoddy built, schools were blamed for the deaths of thousands of children in the Sichuan earthquake last year.