TIME and time again, you will hear Hong Kong's present property boom being attributed to the ''China factor''. So, what exactly is the China factor? Why has Hong Kong benefited so much, and is this trend sustainable? I would argue that it is, for several reasons. Putting political events aside for the moment, China has, in many ways, been Hong Kong's economic saviour over the past decade. In the early 1980s, it was becoming clear to Hong Kong manufacturers that land and labour costs were rising so fast that they would soon be uncompetitive if they remained in Hong Kong. The development of firstly Shenzhen Special Economic Zone, and then the whole of Guangdong Province, as a low-cost manufacturing location, provided a convenient alternative for Hong Kong manufacturers who could move their factories to a location only a few hours from the territory, yet have much lower land and labour costs. In fact, this has worked so well that Hong Kong manufacturers now employ more than three million people in Guangdong Province, far more than they ever employed in Hong Kong. The adverse effects on Hong Kong were minimal because goods still had to be finished off in Hong Kong, which suited the territory's skilled workforce. Hong Kong is still the main route for imports and exports to China. China has also helped Hong Kong over the past few years to open up its domestic market for goods and services. Perhaps most significantly, China has helped Hong Kong to develop the ''socialist market economy'' which has led to dismantling of many restrictions on private business in China. This created an unprecedented surge in demand for offices in Hong Kong, as new companies arrived and existing companies expanded to take advantage of new business in China, which, in turn, saved Hong Kong from the effects of over-bidding in early 1990. Consequently, Hong Kong has avoided the property depression which now affects Singapore, Bangkok, Jakarta, Taipei and Tokyo, and will shortly affect Kuala Lumpur. In the next 10 years, the question is not so much how China's austerity measures will affect Hong Kong, but more a case of will the territory, and perhaps even the mainland, become victims of its success? Accommodation costs in Hong Kong, both offices and residential, are among the highest in the world, and the territory is widely tipped to take over number one spot from Tokyo by 1995. If this position is to be justified, the level of business to be done in Hong Kong must continue to expand at the rate it has achieved over the past few years. A new and unexpected problem is that Guangdong Province is slowly, but severely, pricing itself out of the low-cost manufacturing market, with both land prices and wages now significantly higher than central and northern China, Indonesia, Vietnam, and certain parts of Thailand and the Philippines. Since most of the companies based in Hong Kong are doing business in China, a logical move would be to relocate not only factories, but also offices and staff to China. But China's infrastructure is poor, and likely to remain so for the next decade. More fundamentally, offices and apartment rents in Beijing and Shanghai are not much lower than Hong Kong, at $30 to $45 per square foot per month for offices, and a little less for apartments. There is also a great shortage of suitable accommodation inmost major cities, although the situation is expected to improve in 1995/96 as new projects are completed. Despite the high accommodation costs in Hong Kong, the territory is still the key to China's development, and foreign companies are going to continue to expand in Hong Kong for as long as China's economy continues its phenomenal rate of growth.