Japanese hurler Yu Darvish told home fans Tuesday he was moving to the US major league to pit his skills against better batters because he wanted to become the world's "number one pitcher".

"I want to be the kind of pitcher about whom everyone in the world will say, 'the number one pitcher is Darvish'," he told a press conference at Sapporo Dome stadium, home to the Nippon Ham Fighters, where some 10,000 fans had come to see their hero.

Darvish, who had previously said he had no wish to move to the majors, said he changed his mind because he wanted a new challenge.

He said it had become increasingly easy for him to take on Japanese hitters, and it had got difficult to stay motivated.

The 25-year-old inked a six-year deal worth $60 million last week to join the Texas Rangers' starting rotation.

"I used to feel that Japan provided the best environment for me. But I came to believe that I needed to change that environment and move to the majors," he said.

"As a baseball player, I wanted to fight real battles," he said, adding that he also wished to showcase the quality of Japanese baseball to the Americans.

Darvish, born to an Iranian father and a Japanese mother, joined the Fighters in 2005 after high school and became the highest-paid player in Japanese baseball, earning an estimated 500 million yen ($6.4 million) a season.

Darvish went 18-6 last season with a 1.44 earned-run average and 276 strikeouts in 232 innings.

Standing 6 foot 5 inches (196cm) and weighing 216 pounds (98kg), he has been the strikeout king three times and twice been named the Pacific League's Most Valuable Player.

Darvish has kept an earned-run average under 2.00 for the past five seasons in Japan.