The bill approved on Friday by the Japanese Prime Minister Shinzo Abe's cabinet will now be sent to parliament for debate and is expected to be fast-tracked, Chief Cabinet Secretary Yoshihide Suga said.

Abdication must take place within three years of the bill becoming law. Current Japanese law has no provision for abdication.

Earlier this year reports suggested that Akihito could step down at the end of December 2018 and be replaced by Crown Prince Naruhito on January 1, 2019. Reports of his desire to retire surprised Japan when they emerged last July, and in August he publicly cited age and declining health as reasons why he wished to abdicate.

Akihito was 56 years old when he ascended the throne in January 1989 after the death of his father, Emperor Hirohito. Naruhito is 57.

Constitutional issues

The leading opposition Democratic Party has argued the law should be permanently changed to ensure stable future successions but reportedly approved the current one-off bill after talks with the ruling bloc.

Some scholars and politicians have argued that changing the law to allow any emperor to abdicate would risk Japan's monarchs becoming subject to political manipulation.

The issue has also highlighted concerns over a potential succession crisis in one of the world's oldest monarchies. Only men are allowed to become emperor under current law, though Japan has had empresses in past centuries.

Love match

The royal family is set to lose a member with the coming marriage of Princess Mako, one of Akishino's daughters. When she marries a commoner, she will become one herself.

When Naruhito, who has a daughter but no sons, ascends the throne, his younger brother Akishino will be next in line, followed by Hisahito, Akishino's 10-year-old son.

"The sustainability of the imperial system is in real danger," Takashi Mikuriya, head of the panel, told the Mainichi Shimbun daily in an interview.

jbh/sms (AFP, AP)