Japanese boxing sensation Inoue Naoya, who now holds all four major bantamweight titles, says he will continue fighting until he has reached his physical limit.

Inoue defeated Britain's Paul Butler Tuesday night in Tokyo, flooring his opponent in the 11th round.

Inoue spoke to reporters about the fight and his future on Wednesday at a gym in Yokohama, near Tokyo, to which he belongs.

He became the division's first undisputed champion in the world to unite four major titles. He is also the first Japanese boxer across all weight classes to hold all four major championship belts.

Inoue said it was a great night, and that seeing his four championship belts makes him aware of the significance of his achievement.

He said Tuesday's match was his toughest. He said it took time to defeat his opponent and that he suffered the most muscle pain ever compared to other bouts.

He added he could end his career as the "greatest boxer" if he retires now, but he wants to continue challenging himself to see how far he can go until he has reached his physical limit.

Inoue plans to switch his weight class to super bantamweight. He said he will fight in that division with the aim to win all four titles.