The best free streaming service for cinephiles is the Korean Film Archive’s YouTube channel. It hosts an ever-expanding collection of restored and subtitled films that have been chosen for their outstanding quality and their significance to the history of Korean cinema. Imagine a free US film archive that made available Citizen Kane, Casablanca, Gone With The Wind and The Godfather, as well as a hundred other classics, and you start to see what a gift KOFA’s YouTube channel is to the world.

Among the many great films it offers, one stands out above them all: Obaltan, Yu Hyun-mok’s 1961 masterpiece about life in Seoul in the aftermath of the Korean war. The best way to understand the difference between how Obaltan is regarded in South Korea and how it is regarded in the west is to consider the results of three polls.

In a poll of film-makers held in 1999 by the South Korean newspaper the Chosun Ilbo, Obaltan was voted the best Korean movie ever made. In a 2014 poll of experts organised by the Korean Film Archive itself, the title of greatest Korean film was shared by three movies. They were Ha Gil-jong’s bittersweet campus comedy The March of Fools; Kim Ki-young’s satirical horror movie The Housemaid (which is a favourite of Martin Scorsese’s and the acknowledged inspiration for Bong Joon-ho’s Oscar-winning Parasite); and, once again, Obaltan.

In contrast, when the British Film Institute’s Sight and Sound magazine held the 2012 edition of its prestigious Greatest Films of All Time poll, Obaltan did not receive a single vote from any of the 846 participants. Other Korean classics got votes. Ed Wood’s Plan 9 From Outer Space got a vote. But Obaltan got none. Clearly, this is a film that most audiences in the Anglosphere have yet to discover.

And what a film they will find when they do. Obaltan – often translated as “Stray Bullet” or, perhaps more accurately, as “Aimless Bullet” – is as desolate and atmospheric as any American film noir. It sits alongside The Third Man and some of the major classics of Italian neorealism as one of the great films about peacetime in a city still disfigured by war.

The brilliance of Obaltan’s narrative is that the film focuses on whichever character is most important to the action for as long as they remain important to the action, and then withdraws from them almost completely. Consequently, it takes a while to work out which is the central character.

At first, it seems as if it could be Gyeongsik (Yoon Il-bong), a disabled veteran who now walks with crutches and feels he has lost his place in the world as surely as if he had never returned from the war. Then it appears to be Gyeongsik’s former army comrade, Yeongho (Choi Moo-ryong), who is finding it similarly difficult to fit into civilian society.

Eventually, we see that the character around whom all the others are in orbit is in fact Yeongho’s brother, Cheolho (Kim Jin-kyu), a quiet, dedicated accountant on whose small salary an entire extended family depends. The family lives in Haebangchon (“Liberation Village”), a hillside shanty town filled with families that lost their homes in the war and / or defected from North Korea.

Cheolho’s wife is nine months pregnant. His brother is a liability. His sister is soon to be arrested for prostitution. And his bedridden mother, who has post-traumatic stress disorder or dementia or both, believes bombs are still dropping and repeatedly moans “Let’s go!” or “Let’s get out of here!” – by far the most famous lines in the script – to relatives who have nowhere to go and no way of getting there if they did.

On top of that, he has an incessant toothache he can’t afford to fix. Kim Jin-kyu’s performance is so effective that the pain seeps out of Cheolho’s teeth and into our own. Watching events wear him down is like watching waves relentlessly eroding a precarious cliff.

The most haunting image in Obaltan is one of the most haunting images I’ve ever seen. Driven to crime, Yeongho botches a bank robbery. Chased by the police, he flees through a sewer, where he hears a baby’s cry. The baby, he sees, is bound to its mother’s back. The mother has hanged herself. Yeongho runs on. So do the police officers. The baby continues crying.

The shot of the dead mother’s dangling body is as fleeting, and as unforgettable, as our first glimpse of Orson Welles in The Third Man. Seeing it, we realise – if we haven’t realised already – that the wretched lives we have been following in the film are not unusual. Everyone in post-war Seoul has a story of suffering, and the city is indifferent to them all.

• Obaltan is available worldwide on YouTube