The city of Naha in Okinawa Prefecture launched a system of certifying same-sex marriages Friday, becoming the fifth municipality in the nation to introduce such a system.

Couples of the same registered sex aged 20 or older residing in Naha will be eligible to apply. The mayor will check the application form and resident registration documents, and issue a certificate in about a week, according to the Naha Municipal Government.

Naha officials said they expect couples to use the certificates when applying for a room in municipal housing or filling out documents at medical institutions.

The city started accepting application reservations Friday. An application form can be downloaded from the city's website and can be submitted starting Monday.

Tokyo's Shibuya and Setagaya wards launched similar systems in November, followed by Iga, Mie Prefecture, and Takarazuka, Hyogo Prefecture. Some major companies introduced in-house rules to treat same-sex couples equally with married couples.