TOKYO (AFP) - The wedding of Princess Mako, the eldest granddaughter of Emperor Akihito, and her college sweetheart will be postponed until 2020 due to a lack of "sufficient preparations", news reports said on Tuesday (Feb 6).

Princess Mako and Kei Komuro, both 26, had been scheduled to become formally engaged in a traditional court ceremony next month before their wedding on Nov 4.

But the couple have decided there was not enough time to make "sufficient preparations", Princess Mako said in a statement quoted by Jiji Press.

They have already informed the emperor and empress that their wedding-related ceremonies will be delayed until 2020, since the imperial family's schedule will be tight next year as Emperor Akihito abdicates, Jiji said.

"I'm very sorry for causing a big trouble and extra burden to those who have sincerely helped our wedding," Princess Mako said.

An imperial household agency official said the couple still want to get married and denied any connection between the postponement and a recent magazine article about alleged money trouble involving the fiance's mother, Jiji reported.

The emperor shocked the nation in 2016 when he signalled his desire to take a back seat after nearly three decades in the job, citing age and health problems.

He will leave the post on April 30, 2019 - the first time for more than two centuries that a Japanese emperor has stepped down.

Emperor Akihito's eldest son, 57-year-old Crown Prince Naruhito, is set to ascend the Chrysanthemum Throne a day later.

Princess Mako is the eldest daughter of Prince Akishino, Crown Prince Naruhito's brother, and Princess Kiko.