SINGAPORE - The stars of G Storm, Louis Koo and Jessica Hsuan, went through memorable shoot-outs, car chases and explosions for the action thriller movie.

It is the last film in the Storm series, which tells the stories of officers working for the Independent Commission Against Corruption (ICAC) in Hong Kong. It opens here on Dec 31.

Here are five things to know about the movie.

Real guns

G Storm, the sequel to P Storm (2019), is the fifth and final instalment of the Storm series, which began with Z Storm in 2014. And it holds no punches, promising to have more action sequences than any of the previous films.

Koo, who reprises his role as anti-corruption investigator William Luk, says real guns were used in G Storm.

"With technological advancements, you don't have to use real guns, but I prefer it because I'm more used to it," the 51-year-old star says in a video conference call with local media.

He adds that the most difficult scene to film was a major shoot-out sequence.

"It took two weeks to film. We were filming on the street, so we had to tell members of the public that we were going to shoot guns while running around and we had to take care of their safety. Thankfully, no one was hurt," he says.

Explosive action

Both Koo and Hsuan were involved in various thrilling action scenes throughout the movie. A replica of the Hong Kong Space Museum's planetarium was built for a climactic scene involving multiple explosives.

Hsuan, 51, plays a judge, a character new to the franchise. She says: "The shoot-out and explosions in the planetarium and another extended car chase made me nervous, but not because I was worried about hurting myself. I was worried that I might hurt others."

Running in heels

Hsuan had sprained her leg before filming began.

She says: "I was quite worried because there were so many scenes of me running around in stilettos. I can usually do it, but it's harder with a sprained leg. Thankfully, near the second half of filming, where a lot of the action scenes were concentrated, I was already largely recovered."

Stressed out by Koo

Hsuan and Koo have acted together so many times - including in crime thriller A Witness Out Of The Blue (2019) and wuxia science-fiction series A Step Into The Past (2001) - that they themselves have lost count. While they say they are extremely comfortable working with each other, Koo was stressing out Hsuan at one point.

She recalls with a laugh: "There's a scene in which I slice fruit angrily and when I first filmed it, Louis watched it, but wasn't happy with it. So he told me how to do it, he even demonstrated how he wanted me to act.

"After I finished the scene, I watched his expression to see if he was okay with it, but I think he had given up by that point."

Two endings filmed

As G Storm is the last movie in the Storm series, it has the burden of wrapping up ICAC investigator Luk's story.

Koo reveals that he filmed two endings.

He says: "There was an alternative ending, but I chose to stick with the version you'll see in the movie."

He adds that he found it difficult to part with the series, which spans seven years.

"It's been a long time, so the cast and crew really feel like my family."

G Storm opens on Dec 31.