Nearly 100 years after the “unresolved trauma” of the slaughter of thousands of Koreans in Japan in the aftermath of the Great Kanto Earthquake, an ethnic Korean director is to make his third documentary on the subject.

Oh Choong-kong is a second-generation Korean who was born in Tokyo but now lives in Japan’s Ibaraki Prefecture. He made two documentaries in the 1980s about the killing of as many as 10,000 Koreans in and around the Japanese capital after the natural disaster, which claimed an estimated 120,000 lives.

More than 30 years later, however, 62-year-old Oh feels he has to make a third film to ensure the events of 1923 are not forgotten and that history is not glossed over.

“I feel the tragedy of the massacre again when I hear hate speech – such as ‘kill Koreans’ – in Japan again today,” Oh said. “That racism is still there and I want to bring together the knowledge of researchers looking into this incident with the voices of Korean residents of Japan who are working to make sure this is not forgotten and, at the same time, to make equally sure that it is not repeated.”

The Great Kanto Earthquake struck a little over one minute before midday on September 1, 1923, with its epicentre in Sagami Bay. The megathrust tremor had a magnitude of 7.9, triggered a tsunami that reached a maximum height of 12 metres and lasted, according to some accounts, as long as 10 minutes.

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The quake devastated Tokyo and the port of Yokohama to the south, as well as the surrounding prefectures of Chiba, Kanagawa and Shizuoka. The damage was exacerbated by the number of major fires that broke out – most caused by cooking stoves being toppled – and there are stories of people being burned alive as they fled because their feet sank into the melted tar of roads.

Even after the last fires were put out two days later and the aftershocks tapered off, the horror of the disaster was not over for foreigners living in the region.

The government declared martial law and ordered local police forces to make maintaining order and security their top priority. Within hours, however, rumours were spreading that Korean residents were taking advantage of the tragedy to commit arson, loot damaged properties and poison drinking wells.

Even newspapers reported the rumours, driving the vigilantes into a frenzy.

Responding to the unsubstantiated rumours, mobs seized Koreans living in Tokyo and Yokohama and killed hundreds, while soldiers and police officers took part in the killings. The government later estimated that 231 Koreans died at the hands of roving gangs in the first week of September 1923.

Independent reports – and the Korean community – put the figure far higher, although a precise figure will never be known.

Oh embarked upon his first documentary in 1983 while studying at a film school in Yokohama, working with a Japanese classmate to produce Hidden Scars: The massacre of Koreans from the Arakawa river bank to Shitamachi in Tokyo.

The narrative was based on testimonies from Koreans who survived the attacks, including Jo In-seung, who was set upon by firefighters on the banks of the Arakawa in Tokyo. Jo sustained serious injuries when he was stabbed in the leg with a fire hook and recounted his memories of other Koreans being killed.

Part of the story focused on excavations alongside the river in a search for human remains after the bodies had been cremated, Oh said.

Sensing that the entire story had not been told, Oh produced a second film, The Disposed-Of Koreans: The Great Kanto Earthquake and Camp Narashino, in 1986.

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The military encampment at Narashino, in Chiba Prefecture, was the scene of one of the worst atrocities of the slaughter. Some 3,000 Koreans were taken into protective custody at the base, but as many as 1,000 died at the hands of the military or after being forced to leave its confines, effectively delivering them into the hands of the lynch mobs.

Oh said he became convinced to make a third film after meeting Park Boon-soon, the widow of Jo In-seung, shortly before her death in 2014.

The dwindling number of survivors of the atrocities has made his research far more difficult, Oh concedes, but he has been assisted by the release of documents listing around 300 previously unknown victims that were discovered in South Korea in 2013. Japanese citizens’ groups have also provided help with tracing survivors in Japan.

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One of the people he was able to locate is Kang Gwang-ho, the grandson of Kang Dae-heun, who died on September 4, 1923, at the age of 24. Kang was attacked in the village of Katayanagi, in Saitama Prefecture, by a mob armed with spears and swords.

The assailants were later put on trial, during which it was learned that the local government had issued orders for municipal officials to take steps to defend local residents. The order had not, however, dispelled the rumours of crimes committed by Koreans.

“This was a slaughter committed against members of Japan’s colonies here in Japan and clearly a violation of international law,” Oh said. “Yet the Japanese government is still not being completely open about the issue. That means this is an open historical tragedy and an unresolved trauma for all Koreans.”