(M) ****

Director: Juan Antonio Bayona.

Cast: Naomi Watts, Ewan McGregor, Tom Holland, Samuel Joslin, Oaklee Pendergast.

WITH a title as definitive and overwrought as The Impossible, you could be forgiven for thinking this account of the Boxing Day tsunami might have its emotions cranked up to 11.

You'd be right in thinking that. Almost unrelenting in its ability to jerk the tears and gut-punch you with sadness, this disaster movie packs wallop after emotional wallop, almost to the point that it loses its impact as the story progresses.

This melodramatic tendency has attracted some negative reviews, but let's face it - the film deals with a tragedy that killed almost a quarter of a million people. The Impossible has every right to repeatedly turn on the waterworks while its score swells as one family struggles against difficult odds to find each other.

It is based on the real experiences of the Spanish Belón family - anglicised to the Bennett family here - who were visiting Khao Lak in Thailand when the tsunami hit.

After a short introduction to the family members - mother Maria (Watts), father Henry (McGregor), 13-year-old Lucas (Holland), seven-year-old Tomas (Joslin) and five-year-old Simon (Pendergast) - the wave hits and from then on The Impossible is an almost merciless barrage of heart-wrenching emotions.

The tsunami itself is a scary moment masterfully realised and has far more impact than any skyscraper-high wall of water in some Roland Emmerich disaster blockbuster.

When the horrifying spectacle subsides, we are left with the human face of the tragedy. Choosing to follow just one family keeps the story focused amid a sea of sad tales, although the camera often pulls back to show the immensity of the destruction via longshots of apocalyptic wastelands and overflowing hospitals.

There has been criticism that the suffering of the locals is overlooked in the film, but this is one family's story - yes, a white Western family, but that makes it no less valid.

You'd be a heartless cynic if this movie didn't move you. Yes, it's manipulative and wants to move you again and again to the point where it's tiring, particularly by the end when some narrative coincidences pile everything on top of each other to make a melodramatic mountain of a last act.

Watts is outstanding, but so is youngster Holland, who holds his own alongside the Oscar-nominated Aussie. Both roles look draining on every level and they give their all, with impressive results. McGregor's turn is also great - a scene where he phones home to tell his relatives what has happened is a heartbreaker.

"Emotionally draining" is perhaps the best way to describe The Impossible. The tsunami and its immediate aftermath are more terrifying and scarier than most horror movies, while the rest of the film really wants to try and set a record for the number of times you reach for the tissues. The aim appears to be audience immersion, as if The Impossible wants to drown you along with its stars - albeit in your own tears.

There are some clunky lines, the ending feels conveniently timed, and yes, maybe we could have seen more of the impact on the local people, instead of just featuring them as gallant nameless heroes whose only thought is to care for the Western tourists.

But given that the script is written by Maria Belón and based on her own experiences, such quibbles are forgiveable because the movie succeeds on many levels. If you want to know what it was like to survive one of the worst natural disasters the world has ever seen, The Impossible will show you, in all its painful glory.

Just be sure to take a hankie.