Japan's Emperor Akihito turned 83 yesterday, with the country yet to decide how best to revise its laws to allow him to relinquish his throne.

In a customary video message to mark the occasion, he said he was grateful that many people are giving thought to the matter after he had hinted in a rare televised address in August that he wished to step down as he ages.

In his first remarks on the issue since, he said that he had expressed "what has been on my mind over the last few years, reflecting on my years as the Emperor and contemplating on my role and my duties as the Emperor in the days to come".

He added: "I am profoundly grateful that many people have lent an ear to my words and are giving sincere thought to the matter in their respective positions."

An advisory panel convened in September is due to release its report next month after consulting 16 experts. Nine were in favour of abdication, citing factors such as old age and poor health as barriers to monarchs fully performing their duties.

But seven experts opposed it, amid fears that letting emperors abdicate could destabilise an imperial system meant to be independent of politics. An oft-cited scenario suggests an emperor could be forced to step down due to power struggles - the reason laws were revised in the 1889 Meiji Constitution.

The government is thus said to be inclined to adopt a one-time law to allow the popular Emperor to hand over the throne to his elder son, Crown Prince Naruhito, 56. By law, he must reign until his death.

But Japanese media have quoted Emperor Akihito's former classmate and good friend Mototsugu Akashi, 82, as saying he has been told the Emperor hopes for a permanent system, given that successors could face similar concerns.

Yesterday, some 38,588 people attended his birthday address, the Imperial Household Agency (IHA) said. It was the biggest crowd since he ascended to the throne in 1989.

Emperor Akihito, known for his pacifist views, reflected on the year in his birthday remarks, devoting much time to the war dead and his visits to disaster-hit regions.

He recalled the "deeply moving experience" of his first visit to the Philippines in 54 years with Empress Michiko in January. "The friendly relations that our two countries enjoy today have been built over the course of many years and on the sacrifices of numerous Filipino and Japanese people who lost their lives in World War II," he said.

Emperor Akihito also spoke about the "harsh reality of difficult conditions still faced by the people" of Fukushima, Miyagi and Iwate prefectures, which are still recovering from the 2011 earthquake, tsunami and nuclear disaster.

On the late Thai king Bhumibol Adulyadej, who died in October, he said: "I fondly recall the many occasions over the years on which we deepened our friendship."

The Emperor's uncle, Prince Mikasa, died in the same month, at the age of 100, and the Emperor said it had "meant much to me" to have heard the prince share his firsthand experience in World War II.

Despite a busy schedule, the Emperor has found time for pet projects. He co-authored two scientific papers published this year - one on the gobioid fish species, the other on the food habits of Japanese raccoon dogs. And he has shown no signs of easing up, despite his hint at his desire to step down.

An IHA official was quoted as saying: "His Majesty still diligently attends to each of his duties, reading documents into the night and thinking on weekends about what to say at events."