Sammo Hung hobbles into the interview room on a crutch. He sits, looking exhausted and holding a palm-sized electric fan near his face.

For a moment, it is a bit difficult to connect this man with Hong Kong action cinema.

But speaking about his stunt coaching for Louis Koo - one of Hong Kong's current stars - Hung is filled with excitement.

"He fights well. Before the filming, I design the stunts and record the action scenes performed by (stand-in) stuntmen.

"Koo watches the clips and practices them," says Hung, speaking about the upcoming action thriller Paradox.

The movie is set to open across the Chinese mainland this summer.

Paradox, which is the third installment of the Sha Po Lang (referring to three stars in Chinese astrology, capable of good and evil) franchise - a hit action franchise acclaimed for its real fights - marks the return of Hung as an action choreographer.

Hung and Donnie Yen - who became a top martial arts star thanks to the first SPL movie - starred in the 2005 film.

But in the new movie, Hung says that he wants to focus on action. So he chose to go behind the camera.

Wilson Yip, the veteran Hong Kong director known for the biographical martial arts franchise Ip Man, has directed the new movie.

Yip made the first 2005 movie SPL: Sha Po Lang (released in the United States as Kill Zone), but left the director's seat for Cheang Pou-soi in the 2015 sequel SPL 2: A Time for Consequences.

The latest film, set in Thailand, sees Koo starring as a Hong Kong police officer in search of his missing daughter.

Yip says the majority of the scenes were filmed in Thailand.

Besides Koo, the movie features Gordon Lam, this year's winner of the Hong Kong Film Award best actor prize, as well as Chinese mainland actor Wu Yue and Thai action star Tony Jaa.

Both Wu and Jaa, besides American actor Chris Collins, are veterans of action films.

Wu, 41, began to practice martial arts at age 5 and won a "Wuying" title for kung fu athletes at 17. His years as a professional actor in the National Theater of China helped him polish his acting skills.

Jaa, 41, with a Muay Thai boxer father, also started to learn martial arts at a young age and has won a number of honors.

But despite the top talents in the film Hung says the audience these days is not very interested in typical Hong Kong action movies.

The 65-year-old choreographer-actor, who reinvented the Hong Kong martial arts genre, says: "The market is changing."

Now, young actors can earn fame or profit through computer generated imagery.

"So, they feel that practicing martial arts, which is a tough process, is not worth it."

Hong Kong movies were once favored by Chinese mainland viewers, but were overtaken by Hollywood blockbusters and domestic hits produced by mainland studios.

Now, most local talent have shifted focus to co-producing movies with Chinese mainland filmmakers or working for mainland films.