King Norodom Sihamoni left Cambodia on Monday on a four-day visit to Japan to attend the enthronement ceremony of Emperor Naruhito, the Royal du Cambodge Facebook page said.

The post said the King left the Royal Palace for Phnom Penh International Airport to board a flight bound for Japan on Monday morning. He was seen off at the airport by members of the royal family and senior government officials.

Naruhito will be enthroned according to Japanese tradition on Tuesday in a centuries-old ceremony at the Imperial Palace before an audience of dignitaries from nearly 200 countries.

Among the group of world leaders will be royal family members from Asia, Europe and the Middle East.

Naruhito, 59, became the 126th emperor on May 1, the day after his father, Emperor Akihito, abdicated the Chrysanthemum Throne at the age of 85 due to his advanced age and declining health.

Akihito’s abdication marked an end of the thirty-year Heisei era – which translates as “peace everywhere” – that began on January 8, 1989, the day after the death of Emperor Hirohito.

Naruhito’s reign began the era of Reiwa, which the Japanese government said in April is officially translated as “Beautiful Harmony”.

The Japanese Kyodo News agency said King Sihamoni wrote to Naruhito following the new emperor’s accession to the throne to offer his “warmest congratulations” and “best wishes for success in fulfilling Your noble and exalting mission”.

The news agency continued that the King, expressing appreciation for Japan’s substantial development assistance to Cambodia, said he looked forward to working with the emperor “to strengthen the bonds of friendship and partnership between our two countries”.

King Father Norodom Sihanouk visited Japan for the first time in 1953 – the first visit to the Imperial Palace by an Asian king after World War II – and established diplomatic relations between the two nations.

In December 2013, Japan and Cambodia agreed to advance defence cooperation and upgrade bilateral relations to a “strategic partnership”.

Between 1992 and 2017, Japan contributed some $2.8 billion in aid to the Kingdom. Last year, Cambodia exported more than $1.6 billion worth of goods to Japan and imported some $421 million of Japanese goods.

Before departing Cambodia in August, outgoing Japanese ambassador Hidehisa Horinouchi, who had headed the Japanese mission in the Kingdom since 2016, sent a message to the people saying that Cambodia had maintained an average annual economic growth of seven per cent and that bilateral relations between the two countries had made great strides forward.

On the Japanese embassy’s Facebook page, Horinouchi said bilateral trade, direct investment and the organisation of exchange visits had resulted in considerable growth.

He said Japan would always contribute to the promotion of democracy in Cambodia and provide assistance for electoral reforms. It had also invited Cambodian youths interested in politics to learn about experiences in Japan, Horinouchi said.

“Phnom Penh will, in the next few years, have new airports and high-rise buildings sprouting up, as well as new public transportation systems,” he said.

King Sihamoni will stay in Japan for three nights and return to Cambodia on Thursday.