Okinawa Prefecture's election board said Monday that the vote to replace late Gov. Takeshi Onaga will take place on Sept. 30, with issues surrounding a contentious relocation plan for a U.S. base likely to be at the heart of the gubernatorial campaign.

The plan to relocate U.S. Marine Corps Air Station Futenma from a crowded residential area in Ginowan to the less populated coastal district of Henoko in Nago, both of which are on Okinawa's main island, has been a longtime source of controversy in the prefecture.

The 67-year-old Onaga, who was a vocal opponent of the base relocation promoted by Prime Minister Shinzo Abe's government, died of pancreatic cancer Wednesday.

An election was originally set for November, before Onaga's four-year term was to expire in December. Under the election law, a vote must be held within 50 days of the official notification of an incumbent's death.

Abe's Liberal Democratic Party has decided to field Ginowan Mayor Atsushi Sakima as its candidate, while opponents of the base transfer are stepping up their efforts to pick a successor to Onaga.

The official campaign is set to start on Sept. 13.