TOKYO - Japan's ageing Emperor Akihito suggested on Monday (Aug 8) in a rare video message to the nation that a regency be established, but stopped short of saying that he would step down.

"When I consider that my fitness level is gradually declining, I am worried that it may become difficult for me to carry out my duties as the symbol of the State with my whole being as I have done until now," the 82-year-old monarch said in a 10-minute televised address.

"In coping with the ageing of the Emperor, I think it is not possible to continue reducing perpetually the Emperor's acts in matters of state and his duties as the symbol of the State."

He added: "A regency may be established to act in the place of the Emperor when the Emperor cannot fulfil his duties for reasons such as he is not yet of age or he is seriously ill."

Speculation over Akihito's possible abdication has swirled since Japanese media reported last month that the Emperor, who has had heart surgery and been treated for prostate cancer, wanted to step down in a few years.

But under the pacifist Constitution draw up by American forces, the emperor is not allowed to discuss political issues. The Imperial Household Law, which currently does not provide for abdication, will need to be reviewed to allow for such a step and raising such an idea will be considered political as it requires a parliamentary amendment.

Akihito was therefore expected to not state outright that he wanted to step down, which could be interpreted as interfering in politics.

Indeed Akihito said in his message on Monday that even the establishment of a regency "does not change the fact that the Emperor continues to be the Emperor till the end of his life, even though he is unable to fully carry out his duties as the Emperor".

Responding to the Emperor's remarks, Prime Minister Shinzo Abe said: "The Japanese people views with seriousness the message from the Emperor.

"He has expressed concerns over his age in fulfilling his public duties. The government views his deep-felt thoughts seriously and will firmly think about what to do going forward," Mr Abe told reporters at his office.

The government is "considering special legislation" that would allow only the present Emperor to abdicate the throne, the Yomiuri Shimbun had quoted sources as saying in a report on Monday.

The sources added that a blanket revision to allow abdications might destabilise the status of emperors, and that the government wanted to avoid scenarios in the future where an emperor might be forced to step down due to political pressures, or seek to abdicate without a proper reason.

According to a nationwide telephone survey by Kyodo News this month, nearly 90 per cent of respondents said the Emperor is given too much work. More than 85 per cent said abdication should be made legal as an option for the Emperor and his successors.

Emperor Akihito is not believed to have any immediate health issues, although he was hospitalised for bronchitis in 2011, and had heart bypass surgery in 2012.

He has lamented that old age is catching up with him - most recently on the eve of his birthday last December when he said that "my old age has caused me to make small mistakes at official ceremonies".

As and when he retires, handing over the throne to his son Crown Prince Naruhito, 56, he will be the first Japanese emperor in about 200 years to give up the throne.

His father, the late Emperor Hirohito, had reigned from 1926 until his death in 1989, presiding over World War II. The post-war Constitution of 1947 stripped the Emperor of divine status and cast him as a "symbol of the state and of the unity of the people". Emperor Akihito is the first peacetime monarch.

Last year, he performed about 270 official duties, including meetings with foreign dignitaries.

He has also served to unite the country in times of crises, such as the Fukushima and Kumamoto earthquakes, and built Japan's soft power by trying to soothe wartime wounds with former foes - even as Japan's politics edges to the right.

He has consistently expressed remorse over Japan's wartime actions, from a trip to China in 1992 to a speech last year to mark the 70th year of the end of the war.

This is only the second time that Emperor Akihito has made such a national public address - the first being days after the Tohoku Earthquake in 2011, when he urged national solidarity to overcome the disaster.