Released in January, smartphone game Tower of Saviors has attracted more than five million downloads worldwide - with three million from Chinese-speaking users - making it one of the most popular games on both Android and iPhone systems in the two places.

Tsang said a sixth of the downloaders paid to play the game, and its daily average revenue per paid user was US$40. "Starting my own business had always been my dream," said Tsang, 31. "I thought of giving up … but I really wanted to keep doing what I liked."

Tsang, who has a master's degree in civil engineering from the University of Science and Technology, quit his HK$40,000-a-month fund-selling job in June 2008 to start a creative business company with his brother.

With initial capital of HK$60,000 they created a website generating online greeting cards. But more than a year into the business, they were still not making any profit. To sustain the company, Tsang took several part-time jobs such as private tutoring and selling iPhone cases.

It was not until 2010 that he earned a few thousand dollars by designing a Facebook app for a local shopping mall. After making some money creating more Facebook apps such as psychological test games, he decided to take the plunge into the smartphone apps market.

It took him and his team seven months to create Tower of Saviors, during which they worked 14 hours a day. Upon its release, the game became an immediate hit, with 5,000 people playing it simultaneously after just one week. Now, Tsang is partnering with mainland social media giant Tencent to release and promote the game on the mainland.

He will also take the game to this year's Animation, Comics and Games Expo, which begins on Friday.

Already considering the development of his next hit, Tsang said he believed determination was a key ingredient for success.

"There are many opportunities for start-ups here," he said. "But you need to be determined and complain less."