Andy Lau and Donnie Yen attend a Beijing event to promote their latest work in Chasing the Dragon. [Photo provided to China Daily]

To better play the role, Yen recruited a coach to teach him to speak in the Teochew dialect, as Ng was born and raised in Shantou, Guangdong province, where it is spoken.

But Yen decided the movie will not be a simple good-versus-evil story. As one of the movie's executive producers, Yen pondered about his character who is conflicted while trying to be a good husband, brother and a crime boss all at the same time.

With approval from Ng's family, Chasing the Dragon chronicles the rise and fall of Ng, also known as "Crippled Ho", and his complex brotherhood with a corrupt police officer during a time in Hong Kong when Ng controlled the majority of drug trafficking there. He was arrested in 1974 and sentenced to 30 years behind bars.

For Wong, whose films have received mixed reviews in the past, Chasing the Dragon could be a turning point. After the sneak previews held last week in Beijing, the movie got audience praise.

"I had worked hard on the previous titles. I may have wrongly used my diligence," Wong says of some of his past movies that reviewers have criticized.

Chasing the Dragon is a Chinese equivalent of Once Upon a Time in America, the 1984 classic about some New York gangsters, Wong says.

To bring to life the then-lawless, densely-populated slums gathering gangsters in Hong Kong, Wong built a vast set to replicate the Kowloon Walled City, which was demolished in the mid-1990s.

The film also depicts some corrupt British police officers' discrimination against their Hong Kong colleagues, which Wong says he wanted to expose.

"In the past, I would say I don't know if someone asked me what my favorite work is. But now I will give the answer－Chasing the Dragon," says the 62-year-old filmmaker.