After the August 1945 surrender of Japan in the Pacific War, Allied commander in Southeast Asia Louis Mountbatten following negotiations with a Japanese delegation tasked existing Japanese forces in Southeast Asia to maintain law and order until Allied forces could arrive.

The city of Semarang in Central Java was also by then largely controlled by Indonesian authorities in form of the Tentara Keamanan Rakyat (TKR) and the pemuda.

Following negotiations between the Indonesian pemuda, Wongsonegoro (then governor of Central Java), Major General Nakamura Junji (Commander of Japanese forces in Central Java), and Major Kido Shinichirō (Commander of the Semarang garrison), the Japanese garrison at Semarang handed out around 660[13]-700[14] rifles and 1,600[15] between 5 and 7 October 1945.

Later that day, an Indonesian doctor named Kariadi was shot and killed while he was heading to the reservoir to check the water for any poison.

[8] Prior to learning about the massacre, Kido ordered his men to launch an offensive against Indonesian forces at around 2 a.m. on 15 October, though gunshots had been heard in the city the night before.

Afterwards, accounts noted that Kido's men began "fighting mad", taking no prisoners and conducting large-scale executions of captives.

[26] British accounts of the events generally praised Kido's actions, with Tull writing that "the Japanese [...] protected the internment camps from molestation and released numerous Dutch and Eurasian captives".