A Japanese court has ruled the country's ban on same-sex marriage as constitutional - bucking a trend set by courts around the country that had raised hopes for marriage equality in Japan.

The ruling was met with disappointment from plaintiffs and their legal team who had gathered outside the Tokyo courthouse.

Japan is the only G7 country that does not fully recognise same-sex couples or offer them clear legal protection. But it's not an outlier in Asia, where only Taiwan, Thailand and Nepal offer same-sex marriages.

Ayumi Higashi, the judge who delivered the verdict, said laws on same-sex marriage should first be deliberated in parliament, the newspaper Mainichi reported.

Outside the Tokyo courthouse on Friday, the plaintiffs of the lawsuit and their legal team held up signs that read unjust verdict, local media reported.

Shino Kawachi, one of the plaintiffs, told local media that the ruling was difficult to comprehend. What is justice? Was the court even watching us? Were they considering the next generation? she posed to reporters.

Her partner, Hiromi Hatogai, expressed extreme outrage and wondered if the judiciary was on our side. However, she stated they would keep fighting for their rights.

Amnesty International described the ruling as a damaging step backwards on same-sex marriage in Japan. The group's East Asia researcher Boram Jang urged the Japanese government to be proactive in legalizing same-sex marriage to ensure equal rights for all couples.

The verdict is the final decision among six high court rulings on same-sex marriage lawsuits filed between 2019 and 2021, in various courts across Japan. While five courts previously found the ban unconstitutional, they rejected claims for compensation from plaintiffs. The Tokyo high court's ruling marks a notable exception in a series of favorable responses and adds to the urgency for reform.

The cases will next be taken to the Supreme Court.