A Chinese organisation has appealed to Japan's Emperor Akihito to return a 1,300 year-old stele taken from China over a century ago, state media reported.

The Honglujing Stele was "looted by Japanese soldiers early last century from northeastern China", the official Xinhua news agency said, and now sits in "virtual seclusion" in Tokyo's Imperial Palace.

The stone monument, 1.8 metres (six feet) tall and three metres wide, shows that the first king of the northeast Asian Bohai kingdom was given his title by a Chinese emperor from the Tang Dynasty (618-907), the report said.

The China Federation of Demanding Compensation from Japan (CFDC) sent a letter to Akihito and the Japanese government on Sunday via Tokyo's embassy in Beijing, Xinhua reported Monday.

"What we try to recover is not just the relic itself, but also a symbol of international justice," it quoted CFDC president Tong Zeng as saying.

The demand comes with relations between Beijing and Tokyo at their lowest point in years, with a territorial row over islands in the East China Sea rumbling against a backdrop of disputes over history.

It was unclear what impact including Akihito in the letter would have as the emperor has no power under Japan's constitution, and all imperial household property belongs to the state.

The palace grounds are open to visitors on only two days a year, but there is no public access to the building itself, where an Imperial Household Agency official told AFP the stele is kept.

He declined to comment on the demand for its return, saying: "We have not received any official request."

Japan's presence in China and Korea expanded after it defeated China's Qing Dynasty in the Sino-Japanese War of 1894-95 and Russia in the Russo-Japanese War of 1904-05.

The stele was taken from an area Tokyo captured from Russia in the latter war and sent to Japan in 1908, the Xinhua report said.

Xinhua described the CFDC as a "civic group", and said it was established in 2006 to seek "compensation for personal, material and spiritual damage caused by Japanese militarism during the country's aggression against China in the 20th century".

Bohai, also known internationally by Korean spellings including Balhae, Palhae and Parhae, lasted from 698-926 and succeeded another northeast Asian kingdom known as Koguryo.

Both are regarded in Pyongyang and Seoul as ancient Korean political entities, but their history is highly politicised as Chinese scholars have emphasised their cultural, political, ethnic and geographic links to China, angering Korean scholars and officials.

Japan in 2005 gave South Korea a stele commemorating Korean victories against invading Japanese forces in the late 16th century that had been taken to Japan in the early 20th century. Seoul later sent it to North Korea for return to its original location.