Russian director Vitaly Mansky’s 2015 documentary Under the Sun is a brilliant piece of undercover filmmaking. The cinema-verité work manages to show the horrifying workings of the North Korean state without uttering a word of criticism. The most fascinating part, however, is that the film was made legally, with no hidden cameras.

After two years of lobbying the authorities, the director was invited to shoot an officially sanctioned movie in Pyongyang. Once inside the hermit nation, however, he realised he was not going to be allowed to make a film that accurately depicted life in North Korea. Instead, he came up with an inventive way to subvert the process.

On the face of it, Under the Sun – which has screened at festivals around the world, including the Film Forum, in New York – is about eight-year-old Zin-Mi and her journey to join the Children’s Union. The organisation is part of the Kim Il-sung Socialist Youth League, which aims to indoc­tri­nate young­sters with the philoso­phy of “juche” so they become docile – and war-ready – subjects.

Zin-Mi discusses the health benefits of kimchi with her parents, listens to lectures about the heroism of the Great Leader at school, hears an account of the Korean war from a decorated veteran and learns how to dance in military formation.

Except, of course, nothing is what it seems. Every stage of the filmmaking was supervised by state officials who made the participants stick to an authorised script. When Mansky noticed that the officials didn’t stop him filming between takes, he shot footage of their heavy-handed management of Zin-Mi. This documentary is less about a family than it is the making of a propaganda film.

Exact details of the shoot are unclear, but it seems that the officials weren’t concerned about the unauthorised footage because they took Mansky’s hard drive and censored the shots every night. Next day, they would give back the drive with the controversial scenes deleted. Mansky, however, had copied each drive before handing them over.

Many directors would have been too scared to pull such a stunt, but, Mansky says, he became used to working under such conditions when shooting his 2011 film Motherland or Death in Cuba.

Having caused a diplomatic row between Pyongyang and Russia, the director has been invited back to North Korea – and, he says, he has a good idea what would happen to him if he took up the offer.

Under the Sun will be screened on September 6, 11 and 14 at Broadway Cinematheque, in Yau Ma Tei, as part of the 6th Amnesty International Hong Kong Human Rights Documentary Film Festival.