Pike River: an emotional ride for lead actors Robyn Malcolm and Melanie Lynskey

When Robyn Malcolm and Melanie Lynskey arrived in Greymouth, they first sat down for dinner with Sonya Rockhouse and Anna Osborne - the two women they'd been cast to play in the Pike River film.

“Knowing about them and what they have been through over those years, meeting them was kind of scary and huge in the rehearsal room, but they just came in and started cracking dirty jokes,” Malcolm tells RNZ’s Saturday Morning.

“They made it very real for us very early on, and then we went out for dinner that night and just gossed, just got to know each other.”

Pike River follows the real-life fight for justice by Anna Osborne and Sonya Rockhouse, who lost loved ones in the 2010 mining disaster.

Sonya Rockhouse's son Ben and Anna Osborne's husband Milton were among the 29 West Coast coal miners killed by a methane gas explosion at Pike River 15 years ago.

In the following years, the two women banded together and successfully campaigned for the government to re-enter the mine and improve health and safety legislation for miners.

For Malcolm, it was a "no-brainer" to sign on for the role of Rockhouse, alongside US-based Lynskey, who plays Osborne. The film premiered at the Sydney Film Festival in June and will be released in New Zealand next week, starting with a red carpet screening in Greymouth on Monday.

“I remembered when the Pike disaster happened, I’d been connected on the other side to the mining when we went down as part of the Green Party and Greenpeace to protest the mining of national parks down there,” Malcolm tells RNZ.

“I felt such a connection to the story as an individual and as a Kiwi, and then when I found that Mel was playing Anna, it completely sealed the deal.”

The actors spent so much time bonding with the real-life women, they became “this quartet”, says Malcolm.

“They were on set with us most days and despite the fact we were entrusted with their story, a really painful story for them, they had an amazing sense of humour about it. They made it easy for us.”

Back at that first dinner, Malcolm recalls asking the women: “Clearly, what happened at Pike is the worst moment of both of your lives, and you’ve lost so much, but what has it given you?

“And without blinking, Sonya just looked at Anna and said, ‘Her, it gave me her’.”

The actors say they felt it was their duty to sensitively and accurately portray the story of their friendship.

“I felt in meeting Anna and finding out what was important to her, her number one love in life was Milt, her husband. She loves her children so much, but she had met the love of her life. She met this man who was so wonderful to her,” Lynskey says.

“And I really, really, really wanted to honour that and honour the love that she had for him and how much she wanted justice for him.

“And then the other thing is her deep friendship with Sonya. And there's a couple of scenes in the movie where Anna and Milt are together, where I get to try to give like a little sketch of what that relationship and that love was.

“But the heart of the movie and the entirety of the movie is the relationship with Anna and Sonya.”

Director Rob Sarkies shot the film in Greymouth at various sites connected to the tragedy and called on Jacinda Ardern to play her role as Prime Minister at the time.

“You go into that part of the country now and you can just feel it, like the whole landscape, everything sort of quivers with that history,” Malcolm says.

“And you know that they're in there, those men, those loved men, they're still in that ground, and they're not far away.

“And that to me was really just a very powerful thing.”