Japan's Fukuoka District Court ruled on Thursday that not allowing same-sex marriage was "in a state of unconstitutionality", NHK public broadcaster said.

The ruling came a week after another district court said it was unconstitutional to not allow, bolstering hopes of the LGBTQ community in Japan, the only Group of Seven nation without legal protection for same-sex unions.

Five rulings on same-sex marriage have now been handed down around Japan. The Tokyo ruling was similar, upholding the ban on same-sex marriage but saying that a lack of legal protection for same-sex families violated their human rights.

Opinion polls show some 70 per cent of the public supports same-sex marriage, but the conservative ruling party of Prime Minister Fumio Kishida opposes it.

Kishida has remained noncommittal about the issue despite strong pressure from other G7 nations, especially the United States, in the run-up to Japan's hosting of the G7 leaders' summit last month.