Celebrated Chinese film-maker Zhang Yimou's latest film The Great Wall is a CGI-heavy popcorn movie featuring millions of monsters rampaging China's iconic megastructure.

It is a surprisingly commercial endeavour for a film-maker better known for his arthouse sensibilities. This is also the most expensive Chinese film to date, made at a budget of US$150 million (S$217 million).

And it is not even a passion project for the 65-year-old director of acclaimed films such as Red Sorghum (1987) and Hero (2002).

In a recent interview with The Straits Times in Beijing, where he was promoting the movie with its stars, including Matt Damon, he says he is a director-for-hire on the project, brought on board only after the script was almost completed.

"The story came from Legendary Entertainment chief executive Thomas Tull seven years ago and the script was drafted by Hollywood screenwriters," he says.

"When the producers approached me to direct it, they thought I would laugh at it because it's so commercial. But I accepted the offer and they were thrilled."

It was not the money that drew him to the project, he insists. "Directing something just for the pay? That's not my style," he says.

Instead, he is interested in the Chinese-Hollywood co-production as he sees it as the way forward in the business of international movie-making - he believes there will be many more collaborations to come from two of the largest movie markets in the world.

"The world has changed. Just a decade ago, Hollywood would never have come to me to do something like this. But there has been a power shift and Hollywood needs to explore new markets and new stories," he says.

"I feel like this film is a great way to export Chinese culture to the world. It's exciting to see where it will go."

Hollywood has been trying more and more to capture some of the lucrative box-office receipts in China, which has seen tremendous growth over the years. Last year, China accounted for 18.8 per cent of global movie ticket sales.

This has pushed Hollywood producers to alter scripts to appeal to Chinese audiences, such as when Iron Man 3 (2013) added four minutes of extra footage that was shown only in China, which featured Chinese product placement deals, as well as Chinese stars Fan Bingbing and Wang Xueqi.

The Great Wall goes further than that - it was shot entirely in China with a mostly Chinese cast and crew, but in English and with Hollywood's Damon, Pedro Pascal and Willem Dafoe in the mix.

This kind of mega Chinese-Western collaboration comes with inherent challenges.

When the film's trailer was first released and showed Damon in the lead role, it immediately faced a storm of accusations of "whitewashing", which is the practice of replacing roles intended for people of colour with white actors.

Others said it was yet another white-saviour film - similar to The Last Samurai (2003) and 47 Ronin (2013) - each of which featured a white man rescuing an entire Asian population.

Zhang defended Damon's casting, saying the role was written for a Caucasian man from the start and that he was one of five heroes in the film, with the rest being Chinese.

Besides Damon, the film stars Hong Kong actor Andy Lau, Chinese actors Luhan, Lin Gengxin and Jing Tian, as well as Taiwan's Eddie Peng.

The director says: "People jumped to conclusions before the movie came out. I hope that after they watch it, they will see that this is a film deeply rooted in Chinese culture.

"As the director of more than 20 Chinese language films and the Beijing Olympics, I have not and will not make a film in a way that is untrue to my artistic vision."

The monsters in the movie, for one thing, are known as taotie, a mythological flesh-eating beast derived from ancient Chinese literature.

Zhang also reworked the script, removing the romantic subplot between Damon and female lead Jing Tian and adding a grand Chinese funeral scene.

"The Americans thought that the funeral scene was unnecessary, but I wanted to keep it because it showcased the collective Chinese spirit when someone respected dies," he says.

"As for the romance, I felt like it was unconvincing. It is common in Hollywood films for people to start frolicking in bed almost straight after meeting, but I felt like it would be unrealistic here. Damon and Jing Tian have only seven days to know each other - it just wouldn't make sense."

Damon, 46, says in a separate interview with The Straits Times: "No American director could have made this film. Zhang Yimou worked closely with Thomas Tull and that is crucial when you have two cultures creating something together."

He does not want to predict if the film will be a box-office success in the United States when it opens there in February, but he hopes that the film will at least "expose American audiences to a great Chinese director".

"A lot of Americans do not have any exposure to great directors of world cinema, which is a pity.

"Going forward, there will definitely be more big tentpole movies done as international collaborations such as this, but because they are so expensive to make, you want to get the biggest possible audience," he adds.

Damon, who says he has seen almost all of Zhang's films, with Raise The Red Lantern (1991) being one of his favourites, says: "The main reason I jumped onto this film was just to have the chance to work with Zhang Yimou.

"And this is also the first time we've seen any Chinese-Hollywood film on this scale. I think everyone on the project, whether he was from the Hollywood or Chinese side, knew how unique this opportunity was.

"It's like one giant experiment, but I think everyone went into it with a real sense of optimism."

In China, where the movie opened two weeks ago, the film has been a hit, making more than US$69 million on its opening weekend.

Zhang says: "This film needs to succeed at the global box office so that we can take this co-production model further.

"My hope is that a Chinese film can eventually be as profitable as Transformers (2007) or as influential as Star Wars, where audiences from around the world want to see it. But there's still a long way to go."

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•The Great Wall opens in cinemas tomorrow.