In the confusion after the earthquake of 1 September 1923, rumours that Koreans were poisoning wells, setting fires and preparing an uprising were spread and repeated by police and official channels, and martial law was declared. Vigilante groups formed and, together with police and soldiers, killed Koreans and some Chinese and Japanese who were mistaken for them, checking identity by pronunciation at street barricades; the anarchist Osugi Sakae and his partner and nephew were killed by a military police officer, and labour organisers were killed at Kameido. Estimates of Korean deaths range from the Japanese Home Ministry's contemporary figure of about 230 through independent Japanese investigations in the range of 2,600 to the roughly 6,000 recorded by Korean student investigators at the time and repeated in the Harvard-Yenching Institute's account of recent scholarship, which argues the state both induced the killings by spreading rumours and mobilising police and soldiers under martial law and then concealed its role through cursory prosecutions. A small number of vigilantes were tried and received light sentences. Successive Japanese governments have not issued a formal acknowledgement of state responsibility, and in recent years the national government has said it has found no records allowing it to establish the facts, while the governor of Tokyo has declined since 2017 to send the customary memorial message to the annual commemoration.
Vigilante groups, police and army units killed Koreans, Chinese and Japanese leftists in Tokyo, Yokohama and the surrounding prefectures in the days after the Great Kanto Earthquake of 1 September 1923
Japanese Home Ministry registration figures put the Korean population of Japan at roughly 80,000 in 1923, of whom perhaps 20,000-25,000 lived in Tokyo and Kanagawa prefectures, the area of the massacre. Registration was incomplete and some estimates for the national Korean population run higher.
The Japanese Home Ministry's contemporary count was about 230 Koreans killed; the Japanese scholar Yamada Shoji and others working from local records reach figures in the low thousands; Korean investigators at the time compiled about 6,000, the figure cited in the Harvard-Yenching account. Several hundred Chinese labourers and a number of Japanese, including Osugi Sakae and the Kameido labour organisers, were also killed. The disparity reflects the absence of any official investigation, the destruction and non-release of records, and disputes over which killings to include.
The killings, the role of official rumour and of police and soldiers under martial law, and the subsequent prosecutions are documented in Japanese police and judicial records, in contemporary Korean investigations and in the scholarship summarised by Hasegawa and the Harvard-Yenching Institute.
Japan