Emperor Akihito acceded to the throne after his father's death in 1989
Japan's Emperor Akihito has hinted that he may abdicate, saying his age could make it difficult for him to carry out his duties.
In a rare video address to the public, Akihito stopped short of saying he wants to abdicate, but said his "fitness level is gradually declining".
He added: "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.
"There are times when I feel various constraints such as in my physical fitness."
Public broadcaster NHK reported last month that Akihito wants to step down within the next few years.
Such a move would be unprecedented in modern Japan, and no legal procedures exist for an abdication.
The emperor has undergone heart surgery and been treated for prostate cancer in recent years.
Japan's emperor is defined in the constitution as a symbol of the "unity of the people" and has no political power.
Most Japanese citizens sympathise with his desire to retire, although conservatives who back Prime Minister Shinzo Abe are opposed to the move.
A survey by Kyodo News last week showed that 85.7% of people surveyed were in favour of legal changes that would allow an abdication.
Mr Abe, in a response to the emperor's speech, said the government would take the emperor's remarks "seriously".
"Considering the emperor's duties, as well as his age and the burden (of the job), we have to firmly look at what we can do."
The public address marked only the second time Akihito has spoken directly to the nation.
The first was in the days after the March 2011 triple earthquake, tsunami and nuclear disaster as he sought to calm a nation undergoing its worst crisis since World War Two.
Japan's imperial house is said to be the world's oldest hereditary monarchy, and according to legend stretches back some 2,600 years in an unbroken line.