The mooted appointment of the daughter of assassinated US president John F. Kennedy to the high-profile post of ambassador to Japan, was greeted enthusiastically in Japan on Tuesday.

Caroline Kennedy, 55, who was an early supporter of Obama's 2008 primary campaign before he took on and beat Hillary Clinton's Democratic machine, has long been a rumoured candidate for the plum Tokyo post.

Kennedy is in the advanced stages of the selection process, an administration official told AFP. Earlier Monday, both The Washington Post and New York Times reported that she was actively being vetted for the appointment.

Japan's top government spokesman said it would be a "big news" for the country if she gets the nomination.

"Late President Kennedy was a figure familiar to many Japanese," Yoshihide Suga said at a regular press conference on Tuesday.

"It would be big news, and would deepen people's feeling of friendliness (to the United States)," he said, adding that he would refrain from commenting further until a final decision was made.

Kennedy would fit the long tradition of presidents naming high profile envoys to key US ally Japan, who have included former vice president Walter Mondale and former senators Mike Mansfield and Howard Baker.

But she would also take up the post at a time of great diplomatic peril, given North Korea's fierce military threats against the United States and its key regional partners.

The crises had prompted some diplomatic observers in Washington in recent weeks to suggest that Kennedy could be passed over for a more experienced diplomatic hand.

But Kennedy's chances may have been enhanced by the arrival as secretary of state of John Kerry, who was close to Caroline Kennedy's beloved uncle, late senator Edward Kennedy.

The White House and State Department both declined to comment on the reports that Kennedy was close to being named, but did not deny them outright.

While politics and public service runs in Kennedy's blood, she has long resisted the public role of her father, his brothers, Robert F. Kennedy and Edward Kennedy, and many of their progeny.

For a time in late 2008 and early 2009, she toyed with the idea of running for the New York Democratic Senate seat vacated by Hillary Clinton when Clinton became Obama's first-term secretary of state.

But the wealthy Kennedy pulled out after a rough political ride amid claims she was being foisted upon the New York electorate with nothing but her family name as a qualification.

Kennedy, whom many Americans remember as a tragic little girl at her father's 1963 funeral at Arlington National Cemetery, caused a sensation in 2008, and fury in Clinton circles, when she broke from her intensely private world to back Obama.

In a New York Times column titled "A President Like My Father" Kennedy wrote of never having seen a president who matched up to the way people still talked about JFK.

Now, she said, "I believe I have found a man who could be that president."

If nominated, and confirmed by the Senate, Kennedy would succeed current US Ambassador to Japan John Roos, a former Obama campaign donor.