The disaster film genre can be a real spectacle, such as classics like 1972’s The Poseidon Adventure and 1974’s The Towering Inferno.

They seem to be fairly thin on the ground in recent years – ones worth watching that is – with the genre mostly overlooked and ignored.

This South Korean makes a splash in the right direction, before it reveals its hand to have another genre under the surface.

Waking up in her apartment with her son Ja-In (Kwon Eun-sung) is An-Na (Kim Da-Mi). She’s about to get him ready to send him off to school, when she notices the weather is quite bad, with heavy rain outside.

It’s only minutes later when she realises that there’s water on the floor, and she looks out the window to confirm that there’s a flood outside and the water is getting higher and higher.

There’s an announcement in her building, encouraging all residents to make their way to the roof – ASAP – which An-Na responds to.

She starts to go up the stairs, but realises it’s going to be difficult as everyone else is trying to do the self same thing.

The more she attempts to escape with her son, the more she realises that the flood is the least of their problems, with other dangerous factors at play.

For at least half its runtime, Byung-woo Kim’s film is an outstanding disaster film, as a young mother and her son try to escape the building is a thoroughly thrilling watch.

The director, who also co-write the script, wasn’t satisfied with it just being a disaster film, as it morphs into...something else; not only does it absorb another genre – sci-fi – but there’s more than a whiff of two other films - Tron and Groundhog Day. Altogether they make quite strange bedfellows, but still work – sort of.

Perhaps where it disappoints is in not just being a disaster film, which it excels at for the first half. It’s a premise that audiences would have been more than happy to surf along with, but just like a tide, the narrative turns, in what many might find a disagreeable direction.

The sci-fi aspect gets turned all the way up to eleven, with technology playing a major role, which makes it a bit of a head-scratcher, no doubt followed by widespread “huhs?!” by all who watch it.

It kind of makes sense, which is supported by a brave performance by Kim, who spends so much time wet and in the water, she must have gotten very wrinkled while shooting, as well as get through a whole lot of T-shirts.

It is then, a film of two halves, which will please fans of disaster films and sci-fi, but if you were hoping for an all out disaster film, - as the title and poster material hint at – you will no doubt feel a sinking feeling by the end of it.