One of the best sources for making money was leeching off of China. Because China is so far away from the US, they can't easily trade there. However, Britain is much closer to the United States. They traded with China for goods and then traded those back to the US for a large profit. This was especially true when the US declared embargo on China, when people could still buy things from Hong Kong.
But trade with China wasn't Hong Kong's only source of money. During British rule, Hong Kong became a center for financial services such as banking, based mainly between the Hong Kong and Shanghai bank and companies such as Jardine Matheson, a set of Asian-based businesses. Most of the economy was based on shipping, banking, and merchant companies, but as the population doubled repeatedly, they branched out to supply services and stores to cope for the amount of people. Also, because of the shipping across seas, they gave shipbuilding and maintenance. Other advancements in economy in the 1800's were making sugar, cement, and even ice cream.
In the 1900's, however, things didn't start well. With the wars in China and World War II, there was very little Hong Kong lost a lot. Because trade is Hong Kong's best way to get money, and the war stopped people from trading (especially China, with the Japanese invading), Hong Kong went into a slowdown of all trade whatsoever. Luckily, the problems in China sent businesses and entrepreneurs to the safety of Hong Kong.
After the war China began to separate itself from world trade, partly because of the embargo declared by the US in 1949 and then the UN in 1951. This meant that Hong Kong couldn't depend solely on China. So, Hong Kong industrialized and began to export products, mainly textiles, but diversifying into clothing, electronics, and plastics by the 1960s.
This graph shows the amount of money made in Hong Kong in GDP. GDP stands for Gross domestic product. There's a large equation to find it,
but it is essentially the amount of money earned in one calendar year by the entire country. As You can see, services topped out at 100,000 million dollars in 1992, but manufacturing and trade reached about three times as much.
However, in the 1980s and 90s, Hong Kong started to shift away from selling things like clothing and plastics to services like banking and commercial services. As you can see in the graph above, manufacturing kept expanding until 1992, when it started to decline. In contrast, look at the line for money made from services. Overall employment in services was about 80%. From 1982 to the 1990s, the average amount of the population in unemployment was 2.5%.