Taketoyo Toguchi, 56, narrowly won the vote in the town of Nago in the Japanese island's north, preventing Susumu Inamine, 72, from serving his third term as mayor, the local election board said.

Inamine is a strong opponent of the joint project by the US and Japanese governments to move the US Marines' Futenma Air Station from an urban area in the south of Okinawa to a coastal district near Nago.

Toguchi, supported by Abe's Liberal Democratic Party and its coalition partner Komeito, has not openly discussed his position on the relocation plan, pledging to boost the city's tourism instead.

However, local media dubbed the race a "proxy war" between anti-US base Okinawa governor Takeshi Onaga and the Tokyo government under Abe, as the mayoral vote is seen as a precursor to Okinawa's gubernatorial election later this year.

Japan and the United States agreed to move the base from the town of Ginowan to the Nago coast in 1996 but the plan never went ahead due to opposition from many residents of Okinawa, which hosts the bulk of some 47,000 US troops based in Japan.

Opponents support the removal of the US base from Ginowan but want it relocated out of Okinawa altogether.

The base is located next to an elementary school which recently saw a window from a US military helicopter fall onto its grounds while children were taking a sports class.

Just two weeks ago, an American military helicopter made an emergency landing on a remote island in Okinawa prefecture -- the latest in a string of accidents that have fuelled local opposition to the US forces.

Last month, US Secretary of Defense James Mattis apologised to his Japanese counterpart Itsunori Onodera for the incidents.

A series of crimes including rapes, assaults, hit-and-run and drink-driving accidents by US personnel have also triggered protests on Okinawa, and are a frequent irritant in relations between close security allies Japan and the United States.

In Sunday's election, Toguchi won 20,389 votes to beat Inamine, who received 16,931 votes.

Okinawa was the site of a major World War II battle that was followed by a 27-year US occupation of the island, and it would serve as a launchpad for any American military activity in Asia.