Japan's Naoya Inoue became the first undisputed bantamweight world champion in half a century on Tuesday after stopping England's Paul Butler in the 11th round in Tokyo.

The unbeaten Inoue, nicknamed "Monster", finally floored a defensive Butler with a flurry of body shots after dominating the bout.

Inoue took his record to 24-0, with 21 knock-outs, and added Butler's WBO title to his own WBC, WBA and IBF belts.

He becomes the first undisputed bantamweight world champion since Panama's Enrique Pinder in 1972.

He also becomes only the ninth undisputed world champion since the four-belt era began in 2004, and the first in the bantamweight division.

Inoue has long set his sights on unifying the bantamweight titles and has said he intends to move up to super-bantamweight after accomplishing his mission.

The 29-year-old started in characteristically ferocious fashion against Butler, landing several big shots in the opening round.

He unleashed a volley of body shots in the second, Butler barely able to return fire with Inoue in full control.

Inoue continued to punish the Englishman through the early rounds, connecting with a series of punches after trapping him in the corner on two occasions.

Butler drew deeper into his defensive shell as the match wore on and Inoue grew frustrated as he tried to coax him into launching an attack.

But the Japanese fighter continued to inflict damage and finally floored him 1min 9sec into the 11th round.

Inoue joins an exclusive club of undisputed world champions in the modern boxing era.

He is only the ninth fighter to hold all four belts from the major sanctioning bodies — WBC, WBA, IBF and WBO — at the same time.

The eight others are Bernard Hopkins (middleweight), Jermain Taylor (middleweight), Terence Crawford (super lightweight), Oleksandr Usyk (cruiserweight), Josh Taylor (super lightweight), Saul Alvarez (super middleweight), Jermell Charlo (super welterweight) and Devin Haney (lightweight).

Inoue became the first Japanese boxer to top Ring Magazine's prestigious pound-for-pound rankings as the best fighter across all weight divisions earlier this year.

That accolade came after he had demolished Philipinnes veteran Nonito Donaire inside two rounds in his previous fight in June.

Butler, who was fighting away from home for the first time, saw his record drop to 34-3.

Inoue's younger brother Takuma also won on Tuesday's undercard, stopping Jade Bornea of the Philippines in the eighth round.