Japanese baseball superstar Shohei Ohtani kept fans guessing Friday on the identity of his new wife, saying only that they met "three to four years ago" and got engaged last year.

The 29-year-old Ohtani, who signed a $700-million deal in December with the Los Angeles Dodgers, dropped the bombshell on Thursday that he had tied the knot.

In an Instagram post that had 2.86 million likes as of Friday, he said he had begun "a new life with someone from my native country of Japan who is very special to me and I wanted everyone to know I am now married".

Speaking to reporters in Arizona, where the Dodgers are in spring training, Ohtani revealed only that his wife is "a normal Japanese person".

"We first met around three to four years ago. We got engaged last year," he said, calling her "fun to be with".

Asked why he decided to make the announcement, Ohtani said with a laugh that it was because the media "all are very loud and nosy".

"Had I chosen not to make the announcement, then that could have caused lots of talk too. So I wanted to announce that here today so I can focus on baseball from now on," he said.

Ohtani, nicknamed "Sho-Time", has achieved stratospheric fame in Japan and abroad with his skills as a batter and a pitcher, and helped his country win last year's World Baseball Classic.

The high-school baseball prodigy signed with the Hokkaido Nippon-Ham Fighters in 2013 and spent five seasons there before joining the Los Angeles Angels.

There he won two American League Most Valuable Player awards in six seasons but left last year for free agency.

Following weeks of frenzied speculation, he joined the Dodgers in December. His 10-year deal was the richest contract in the history of North American sport.

He made his Dodgers pre-season debut on Tuesday, smashing a home run in his new team's win over the Chicago White Sox.

He said his marriage made no impact on his career decisions.

"She respects my views and opinions, so that is absolutely separated from everything related to baseball. She was willing to come to wherever I was playing," he said.

In his Instagram post, which included a picture of his dog -- but not his bride -- Ohtani said the couple were "still immature in many ways, but we would appreciate your kind support".

"The two of us (and our dog) will support each other and we hope to move forward together with all of our fans," he wrote in Japanese.