The non-binding vote will be held on February 24, with Governor Denny Tamaki campaigning against the relocation of the Futenma airbase.

The base is currently located in a densely-populated part of the southern island, and has caused frictions with local residents over everything from noise to accidents.

In a bid to resolve the long-running tensions, Prime Minister Shinzo Abe's government has backed a plan to move the base to a coastal area, reclaiming land for part of the proposed new site.

But residents opposed to the move want the base moved out of Okinawa altogether, arguing that the region bears a disproportionate burden when it comes to hosting US military troops in the country.

Okinawa accounts for less than one percent of Japan's total land area, but hosts more than half of the approximately 47,000 American military personnel stationed in Japan.

Noise, accidents, and crimes committed by military personnel and civilian base employees have long angered Okinawans, many of whom want other parts of the country to house bases instead.

But the archipelago's location near Taiwan has long been viewed as having huge strategic importance for US forward positioning in Asia.

And Abe's government has shown little sign of willingness to consider relocating Futenma to another part of the country or otherwise changing the spread of US military forces in Japan.

- 'Precious ballot' -

Tamaki, elected in September after campaigning against the relocation plans, has urged residents to vote.

"It is a very significant opportunity for people in Okinawa prefecture to directly show their will. Please go to polling stations and cast a precious ballot," he told reporters earlier Thursday.

The governor is required to "respect" the vote's outcome if approved by at least a quarter of eligible voters -- around 290,000 votes.

But the referendum is not binding on the central government, and spokesman Yoshihide Suga said Thursday that there were no plans to halt the relocation plan.

Suga declined to comment directly on the referendum and repeated the government's position that it was trying to "ease the burden on the Okinawan people in a clearly recognisable way."

The referendum was initially planned as a yes-no vote on the move, but a "neither" option has been added to the ballot after opposition from several cities with close ties to the central government.

Those cities had threatened to opt out of the vote altogether, but the addition of the "neither" option means the referendum will be held across Okinawa.

The closing of Futenma and opening of a replacement facility at Nago, 50 kilometres (30 miles) away, was first agreed in 1996 as the US sought to calm local anger after US servicemen gang raped a schoolgirl.

But it has been bogged down ever since with local politicians blocking the move in a bid to reduce the American footprint.

Another referendum was held in 1996, with nearly nine in 10 people agreeing that US bases should be "reduced" in the area.