The documentary was completed by co-director Hanna Bilobrava after her fiancee and director Mantas Kvedaravičius was arrested and reportedly killed by Russian forces.
Depicting life within Ukraine's besieged southern port city, Mariupolis 2 has shaken the Cannes Film Festival.
The rare documentary which serves as the last testament of the late Mantas Kvedaravičius chronicles Mariupol's survivors seeking refuge amongst the ruins.
The Lithuanian director was killed on 2 April while filming the project. He was arrested by Russian soldiers when he attempted to leave the city and reportedly murdered.
The film was completed by co-director and Kvedaravičius' fiancée Hanna Bilobrova in record time. It was added to the competition as a late entry in celebration of his life before a special screening last Thursday.
However, a dramatic air show led by the French Air Force at the festival promoting the action feature Top Gun: Maverick became too much for Bilobrova, still raw from Kvedaravičius' death, and served as a bitter reminder of the realities of war.
Speaking at Cannes, the filmmaker said, "We were standing yesterday on the balcony and we heard jets fly in so we almost lay down but bombs did not follow. And this other jet... I started to cry."
"A colleague went downstairs to ask what was happening and (for someone) to explain," Bilobrova said.
"We are used to seeing war as a fiction. Even in the television news, it is presented to us as a fiction. It is a representation. Nobody really shows us the people who live under war".
Mantas Kvedaravičius has shot two other documentaries about Mariupol in 2014 and 2015, as the city was already targeted by the DNR separatists after the Russian annexation of Crimea and invasion of the Donbas.
The last film serving as a sequel to the first two films has no music, no voice-overs, and moves seamlessly between long shots of rubble with images of everyday life.
The 45-year-old's camera follows the group who were holed up in his basement, capturing testimonies or reflections of life before the war.
"I hope that people will think for themselves while watching this movie and make their own decision and make up their own minds about what is important," said Bilovrova.
Fred Ponsard, reporting for Euronews live from the festival said the event "has always had this vocation to be in contact with the burning news and offer an exceptional platform to filmmakers who fight for peace and human rights around the world."
"Watching Mariupolis 2 is to live the war from inside, the fear of bombings and chaos at the height of men and women who have lost everything and even life as the director Mantas Kvedaravičius, killed by the Russian army on April 2, 2022, in Mariupol in Ukraine," Ponsard said.