A Japanese city has registered a same-sex couple as partners under the same address, an unusual step hailed by the men as "groundbreaking" in a country without marriage equality.

In Japan, everyone registers their address with local authorities, and Keita Matsuura, 38, told AFP he used to be listed separately from his partner Yutaro Fujiyama, despite living together.

When the pair moved to Omura, in the southern region of Nagasaki, they told city authorities that they wanted to be registered together, like a married couple would be.

Initially, the city offered to register Fujiyama as Matsuura's relative, but after discussions, they agreed this month to register him like a husband, Matsuura said Tuesday.

Japan is the only G7 nation that does not recognise same-sex unions, and local media said the move was unprecedented.

Although the registration is not the same as legal marriage, Matsuura said he was "surprised and very happy".

"I couldn't stop dancing and smiling," he said.

"I think it's a groundbreaking decision -- a step further than the non-legally-binding partnership system" under which municipalities issue certificates to gay couples, he said.

"I hope this will bring more practical benefits to same-sex couples, and will be a step towards legalising same-sex marriage."

Taiwan is the only place in Asia with marriage equality, and this year Thailand moved a step closer to legalising same-sex unions.

In Japan, opinion polls show growing support for LGBTQ-friendly laws, especially among younger people.

But the ruling conservative party has been reluctant to push ahead with reforms.

Dozens of major municipalities, including Tokyo, now offer partnership certificates that allow same-sex couples to be treated as married in certain areas such as housing, medicine and welfare.

Many big Japanese businesses also offer the same family benefits to LGBTQ and heterosexual employees.

However, a slew of recent court cases on the constitutionality of same-sex marriage in Japan have produced divided rulings.

Japan's 1947 constitution says marriage requires "the mutual consent of both sexes" but it also states that all people "are equal under the law."

AFP

Same-sex couples speak to media at Tokyo metropolitan government as the Japanese capital starts acknowledging same-sex partnerships, Tuesday Nov. 1, 2022, in Tokyo, Japan. The Tokyo Metropolitan Government on Tuesday began issuing certificates recognizing same-sex couples in the Japanese capital, a small improvement toward greater awareness of sexual diversity in a country where same-sex marriage is not allowed. (AP Photo/Mari Yamaguchi)

Japanese city recognises same-sex couple in rare step