The naked Chinese migrant workers were dangling on hooks and ropes from a ceiling in north-east Beijing until a few months ago, when they were bundled up in bubble wrap, crammed into a container and shipped off to London. They are not desperate Chinese peasants seeking illegal entry into the UK. Far from it. Their arrival in Britain is part of a cultural invasion, paid for by the UK's most famous art collector, and signalling a surge of interest in Chinese sculpture, painting and photography. "I have been looking at lots of contemporary Chinese art in the past few years and find that a small percentage of it is world class and as good as the best contemporary art anywhere else," he told the Guardian. "There is a huge gulf, though, between the small amount that is world class and the majority, which is derivative and kitsch." Saatchi is a late but influential arrival. Thanks to a near eightfold increase in the market in only two years, Sotheby's in Hong Kong recorded Chinese contemporary art sales of $21.9m (£11m) in 2006. It is a similar story at auction houses from London to New York, many of which started only recently to offer modern Chinese work but now find it their biggest driver of growth. It has bordered on a frenzy. During the first auction of Chinese contemporary art in New York last April, so many bidders were calling in that Sotheby's ran out of telephones. Among the most sought-after works was Lions, the roaring, guffawing multiple self-portrait by Yue Minjun, which eventually sold for more than half a million dollars. Yue's paintings and sculptures of garishly coloured laughing men are seen as symbols of China's consumer culture. This is one of the central themes for contemporary artists, along with reflections on materialism, the loss of traditional values, environmental destruction and the political legacy of Mao Zedong and Tiananmen Square. Most of the headlines have been made by Zhang Xiaogang, whose giant family portraits and split-focus images from the Cultural Revolution era have generated the biggest interest among buyers. Last April, his Bloodline Series: Comrade No 120 sold for $979,200, almost three times Sotheby's high estimate. It was a record for Chinese contemporary art, but one that lasted only until October, when Saatchi paid £769,600 for another work by Zhang Xiaogang at a London auction. With auction sales of $23.6m last year, Zhang Xiaogang was narrowly second to Jean-Michel Basquiat in the ArtPrice ranking of the 100 top-selling artists. But he was far from alone on the chart. There were 24 Chinese names last year, up from almost none five years ago. This represents a huge change in attitudes and lifestyles. Ten years ago, avant-garde artists were on the fringe of Chinese society. Their works were often banned, exhibitions were shut down and, for most, the sales of their work were barely enough to make ends meet. Today, however, a growing number of artists own villas, foreign cars and apartments. "Cynical realist" Fang Lijun is said to own six restaurants in Beijing and a hotel in Yunnan province. Among the newcomers to the top-seller list is Su Xinping, an artist from Inner Mongolia. Su said the price of his work had tripled in the past three years. "My life has changed a little. I still eat simple food and lead a simple life, but I have a more convenient house and a more convenient car. I have several homes, and I bought a studio in the city last year." Su is one of many artists who struggled after their participation in the Tiananmen Square protests. But now he sees greater opportunities to do the work he wants to do, and to get paid for what it is worth. He received a call from New York recently to say several of his works had just sold for almost $400,000. "I won't get any of that money," he grinned. "I sold those pieces years ago." But he will benefit from now on. "The price for Chinese art was too low before. Even now some fine pieces have not reached their true value." Zhang Dali agrees. "I expect the price will keep rising for at least five years because more and more people want to buy Chinese art, but there are not that many Chinese artists. The demand is increasing, but the supply is limited so the price will keep rising." The reasons for the boom are manifold. The establishment of the Dashanzi art district in Beijing three years ago attracted many foreign buyers, who account for about 80% of sales. A government crackdown on property speculation and unease about stock market prices have also pushed many investors to consider art. But many overseas purchasers are motivated by a desire to grab a piece of history. "I think the rise of the art market is highly related to the rising interest in China," said Jonathan Wong of Sotheby's in Hong Kong. "We observe money comes from all over the world and new buyers keep emerging in every auction." Amid concerns about a speculative bubble, insiders say the boom is a mixed blessing. "For big-name artists, the price of works has gone up dramatically - by 10 to 20 times in some cases," said Brian Wallace, whose Red Gate Gallery was the first to show contemporary works in Beijing. "If you were in it for the money 10 years ago, you would be very well off today. But it is not easy. With all the new entrants into the market, more galleries are taking up more artists. So the overall quality is not as high as before. There are many good artists out there, but a lot of them are now painting for the market - even some of the big names."