Ewan McGregor is casting his mind back to Christmas 2004, and the Indian Ocean tsunami that caused havoc across Southeast Asia. "I remember the news footage, and that feeling of horror about it - that so many people had been lost," he says, sounding almost dazed when we meet in a hotel in London's Mayfair.
Echoing feelings many of us experienced on that tragic day, his bewilderment is understandable: the most destructive tsunami on record killed upwards of 230,000 people across 14 countries, leaving millions more homeless as 30-metre-high waves engulfed coastal areas.
Now, eight years on, comes The Impossible, a film that starkly deals with the tragedy, starring McGregor and Naomi Watts. They play British couple Henry and Maria Bennett, holidaying in Thailand with their three young boys when the wave strikes, sweeping away Maria and their eldest son, Lucas (Tom Holland). Forget about Hollywood disaster movies, though: The Impossible is an altogether different experience - harrowing, authentic, immediate and painful.
"The whole concept of the film was to make people feel the experience of being there," says Spanish director Juan Antonio Bayona, who has traded the supernatural shivers of his 2007 debut The Orphanage for an altogether more tangible horror. "I was not the one who chose the story. The story chose me."
Bayona came to it by way of his producer, who heard a radio interview with a Spanish family who survived the tsunami. Inspired and touched by their miraculous escape, "I realised I had to do the story - and started to work out how to put that on the screen".
After the tsunami, the film cuts back and forth, between the injured Maria and the shell-shocked Lucas, and Henry, trying to find his wife and eldest son amid the carnage and chaos. Written by Sergio G. Sánchez, what's immediately obvious is just how the film benefits from close contact with the real-life survivors. "From the very beginning, they trusted us," Bayona says of the family. "They felt it was the right moment to tell the story, to let us tell the story, and they were very collaborative." So much so, mother María Belon even receives a story credit. "They were there all the time in order to put our feet on the ground, as a reminder of what happened there," the director says, "and that was very helpful."
The Impossible is not the first film or TV drama to depict the tsunami or its effect on people. In 2006, BBC drama Tsunami: The Aftermath took a hard-hitting look at some of the characters caught up in the devastation. Fabrice Du Welz's Vinyan (2008) is a surreal portrait of a couple searching for their child, lost in the disaster. And most spectacularly, Clint Eastwood's Hereafter (2010) begins with Cécile de France's journalist engulfed by the wave in Thailand (a scene so traumatic, the film was pulled from Japanese theatres when that country was hit by the tsunami in 2011).
Yet zeroing in on one family lent The Impossible a credibility that, perhaps, some of its predecessors lacked. "The Thai people … were supportive," Bayona says. "We never had any impression that they were questioning the film. For example, we shot in the same hospital where the story takes place. And they were grateful to us for shooting the movie. They thought it was the perfect moment to talk about this story." He pauses. "I think whoever sees the film will see this is our intention - to pay the maximum respect to the people who were there."
That said, The Impossible has been criticised by some reviewers for focusing on foreign tourists, rather than the Thais who had their lives, homes and livelihoods destroyed. Should it have given them a voice?
"One of the things I'm most proud of is how the film reflects how grateful all the survivors are with all the Thai people," Bayona says, noting the scene where Maria is cared for by Thai villagers. McGregor concurs. "People spoke with great fondness about the Thai people and how organised and cleverly they dealt with the situation - and I think we show that."
Certainly, Bayona's film is affecting viewers, from the jaw-dropping 10-minute recreation of the tsunami to Watts' heartfelt performance. The 44-year-old star has already been nominated for a Screen Actors Guild award and a Golden Globe, and a second Oscar nomination of her career (after 21 Grams) seems likely. Last month, Mark Ruffalo - Watts' co-star in 2004's We Don't Live Here Anymore - wrote a piece for industry trade paper Variety proclaiming her "one of our acting treasures", adding "Naomi fills every moment onscreen with honesty and intention".
And in an open letter to Watts, written for American magazine Entertainment Weekly's "Consider This" series, Reese Witherspoon admitted to having been "blown away" by The Impossible and called its lead actress - who she confessed to barely knowing (they've never worked together) - "the life-breath" of the work. Comparing the impact of Watts' performance to when she first saw Meryl Streep in her Oscar-winning role in Sophie's Choice, Witherspoon added, "If I have anything to do with it (and I will literally tap dance on Sunset Boulevard for you!), you will be holding every beautiful statue that exists by the end of February".
While Watts is likely to face some stiff competition in the awards season - not least from Jessica Chastain (for Kathryn Bigelow's Osama bin Laden movie, Zero Dark Thirty) - hers is a brave, committed turn. She spent a month filming the tsunami sequence, when Maria and Lucas are torn away from their family, in a giant tank in Alicante, Spain. Not a strong swimmer, "a lot of it was no acting involved because you're literally being thrust and sucked under, and you're genuinely gasping for air", she says.
It took six special effects companies one year to create this sequence, blending footage from the tank with material shot at the Khao Lak Orchid Beach Resort where María Belon and her family had been holidaying. The production dressed the resort to look exactly as they had left it: torn to shreds. "That must've been very shocking" for the family because they were there for the shoot, McGregor says. And the 41-year-old actor admits that when he learned Belon's two youngest boys were used as extras, covered in blood and mud, "I found it very peculiar".
Watts, however, found it helpful to meet Belon at the Thai resort. The film is part of an ongoing cathartic process for the family, she says. "They have to [talk about it], because it's a way of understanding it." It was the same with the local people; much in the way the surrounding wetland had changed in the aftermath, the emotional scars were still evident. "Like any massive disaster, people are still trying to process it. The need to talk about it never goes away."
While The Impossible is a visceral depiction of the disaster and its impact, according to Bayona it eclipses that. "Maria was telling me that the whole film is not about the tsunami; it's about the moment when devastation gets to your life. This is the inspirational thing about the story - it talks about the tsunami but goes beyond that and talks about human beings."
He sees it as being about survivor's guilt. "This film is about how to go through an experience where you survive at the end. It's not about survival, but the price that you will pay for surviving."
The Impossible opens on Thursday