Official campaigning started Sunday for the mayoral election in Ginowan in the southern Japan prefecture of Okinawa, with a contentious plan to relocate a key U.S. military base from the city taking center stage.

Former Deputy Ginowan Mayor Masanori Matsugawa, 65, and company executive Harumasa Nakanishi, 57, a former head of a union of Okinawa high school parent-teacher associations, are the contenders in the Sept. 30 election to fill the post vacated by Atsushi Sakima, who is contesting the gubernatorial election being held the same day.

The outcome of the two elections could influence the future of the plan to move U.S. Marine Corps Air Station Futenma from a crowded residential area in Ginowan to the less populated coastal district of Henoko in Nago, also in Okinawa.

Backed by the ruling Liberal Democratic Party, Matsugawa is seeking the prompt closure of the Futenma base due to safety concerns and the return of its land to Japan. But he has not clarified his stance on the plan to relocate the base to Nago.

"(The Futenma base) is located in the center of our city and we're living in severe conditions. I will resolve this problem," Matsugawa said in his first campaign speech.

(The Futenma base)

Nakanishi decided to run in the mayoral race after being tapped by local members of the opposition Japanese Communist Party and the Social Democratic Party. He has expressed his opposition to relocating the base within the prefecture.

The Futenma base "is disturbing our lives and preventing our economic growth and I demand its immediate closure. But I oppose the new base in Henoko," said Nakanishi at a rally to kick off his campaign.

According to a Japan-U.S. accord, land used for the Futenma base will be returned to Japan once the relocation is complete. But construction of the replacement facility in the Henoko district has met with stiff local resistance.

Official campaigning for the gubernatorial race has already started. The election will choose the successor of Takeshi Onaga, who was a staunch opponent of the base relocation plan and confronted the central government before his death last month.

(Base construction site in Henoko)