Two boxers in Japan have died from brain injuries they incurred in separate bouts during the same event in Tokyo, officials said. 

Super featherweight Shigetoshi Kotari and lightweight Hiromasa Urakawa, both 28, fought on the same card in Tokyo's Korakuen Hall on August 2. 

Both were later rushed to hospital where they had brain surgery. 

Kotari, who battled to a draw after 12 rounds against fellow Japanese fighter Yamato Hata lost consciousness soon after and "passed away at 10:59 pm on August 8," his M.T boxing gym said on its website Saturday. 

"He did his best to fight his way through the surgery and treatment he had been receiving at a Tokyo hospital due to acute subdural haematoma," the gym's post said. 

Urakawa was stopped in the eighth and final round against Yoji Saito and "tragically succumbed to injuries sustained during his fight", the World Boxing Organization (WBO) said in an Instagram post on Sunday.

Urakawa died on Saturday night, according to local media reports.  

"This heartbreaking news comes just days after the passing of Shigetoshi Kotari, who died from injuries suffered in his fight on the same card," the WBO said, adding it extends "our deepest condolences to the families, friends, and the Japanese boxing community." 

Tsuyoshi Yasukochi, secretary-general of the Japan Boxing Commission, told local media after their hospitalisation that it was likely "the first time in Japan two fighters underwent skull-opening surgery for injuries stemming from the same event".