The Great Kantō earthquake (関東大地震, Kantō dai-jishin; Kantō ō-jishin) struck the Kantō Plain on the main Japanese island of Honshū at 11:58:44 JST (02:58:44 UTC) on Saturday, September 1, 1923. Varied accounts indicate the duration of the earthquake was between four and ten minutes. Extensive firestorms and even a fire whirl added to the death toll. Racist civil unrest after the disaster (i.e., the Kantō Massacre) has been documented.

The earthquake had a magnitude of 7.9 on the moment magnitude scale (Mw ), with its focus deep beneath Izu Ōshima Island in Sagami Bay. The cause was a rupture of part of the convergent boundary where the Philippine Sea Plate is subducting beneath the Okhotsk Plate along the line of the Sagami Trough.Since 1960, September 1 has been designated by the Japanese government as Disaster Prevention Day (防災の日, Bōsai no hi), or a day in remembrance of and to prepare for major natural disasters including tsunami and typhoons. Drills as well as knowledge promotion events are centered around that date as well as awards ceremonies for people of merit.