Voting began on Sunday for a mayoral election in the Okinawan city that is home to a U.S. airbase whose planned move has set Tokyo and Okinawa at odds, with the central government giving strong backing to the incumbent.

Prime Minister Shinzo Abe's government has dangled prospects of a bigger budget for Okinawa, backing for a Disney resort and promises of aid for impoverished children in Japan's second-poorest prefecture to boost the current mayor's chances.

Defeat would boost resistance to moving the Futenma base to the less populated Henoko area of the island, as agreed with key ally the United States two decades ago, and could pose problems at a time when U.S.-Japan ties are more crucial than ever given China's increasing assertiveness in the region and an unpredictable North Korea.

The opposition candidate in Ginowan, like the governor and many voters in Okinawa - which was the site of Japan's only land battles in World War Two and resents hosting the majority of U.S. troops in Japan - wants the base off the island altogether.

Ginowan mayor Atsushi Sakima has played up his ties to Abe's government, and the ruling Liberal Democratic Party (LDP) has sent Shinjiro Koizumi, a telegenic lawmaker popular with unaffiliated voters, to campaign for him.

Tokyo said in December it would boost Okinawa's budget by 1 billion yen ($8.5 million) to 335 billion for the coming fiscal year, after cutting it last year in reaction to the election of anti-base governor Takeshi Onaga, and has backed plans to build a resort on the Futenma land once the base moves.

A win by Sakima still won't guarantee that all goes smoothly with the base move, but a loss would make it even harder, annoying Washington and denting Abe's image six months before an election for parliament's upper house.

"The prime minister's office is throwing everything at this election and if they lose, they've set themselves up to seem like quite a failure," said Sheila Smith, senior fellow for Japanese Studies at the Council on Foreign Relations.

"It would be a delicious political victory for Onaga and demonstrate that he's got more political muscle in Okinawa than the central government."