Powered by Chinese smartphone users splurging billions on mobile games and online shopping, China's tech giants Tencent and Alibaba are racing up the elite league of the world's most valuable companies.

Hong Kong-listed Tencent, famous for its games and WeChat messaging service, became the first Asian firm to break into the $500 billion league last week -- briefly overtaking Facebook as the world's fifth biggest company in terms of market value.

Alibaba is just a few billion shy of joining its Chinese competitor at the top table of public listings -- and is already there when taking into account its private affiliates.

While the top five -- Apple, Google's parent company Alphabet, Microsoft, Amazon and Facebook -- thrive across the world, the two Chinese firms have made their fortunes by cornering China's own vast market of 750 million internet users.