Former Naha mayor Takeshi Onaga hugs his daughter as they celebrate his victory in the Okinawa gubernatorial election in Naha. (Jiji Press/AFP/Getty Images)

Voters in Okinawa have, by a landslide, elected a governor who vows to block the relocation of a controversial ­Marine Corps air station, delivering a setback to both Tokyo and Washington by throwing a wrench into their defense alliance.

Although it is not clear whether Takeshi Onaga will be able to make good on his campaign promise to stop a new base from being built in the Japanese island prefecture, his overwhelming victory is sure to complicate American and Japanese plans to do so.

Onaga has said that he will review the process that led to the approval of the relocation project, and he will be a welcome ally to the local mayor, vowing to do everything he can to stop construction.

“My victory clearly shows prefectural residents’ will not to let the base be built,” Onaga told reporters Sunday night, adding: “I’d like to convey the message to the governments of Japan and the United States.”

A conservative former mayor of the Okinawan capital of Naha, Onaga said he would “act with determination” to overturn the approval to begin a huge landfill project that is central to the base relocation plan.

With 360,000 votes, he had a 100,000-vote lead over his former boss, Gov. Hirokazu Nakaima, who had been backed by Prime Minister Shinzo Abe and his ruling Liberal Democratic Party.

But voters were angry that Nakaima had gone back on his previous pledge to block the base relocation and appear to have punished him for giving it the green light late last year. Abe’s government in Tokyo has vowed to continue with the relocation, saying that one prefecture cannot decide matters of national ­security.

Onaga had a simple campaign promise: no new U.S. military bases­ in Okinawa and no new Ospreys, the noisy aircraft that are widely viewed in the prefecture as dangerous. He vowed to stop the planned relocation of the Marine Corps air station at Futenma — in the middle of the most crowded part of Okinawa’s main island — to a more remote location farther north, in an area called Henoko.

The relocation would involve a landfill project to build two runways out into the sea, which locals say would destroy the environment on land and in the water, as well as bringing noisy aircraft to the relatively undeveloped area.

The base should be moved outside Okinawa, Onaga said, with other parts of Japan helping to bear the burden of the country’s security alliance with the United States.

“Okinawa has suffered a lot. Why do we have to suffer more?” Onaga told The Washington Post before the election, adding that the prefecture comprises 0.6 percent of the Japanese land mass but houses 74 percent of U.S. military bases in the country.

In Nago, the area that includes the proposed new base at Henoko, Mayor Susumu Inamine was eagerly anticipating Onaga’s victory.

“It’s going to be huge for us,” Inamine said in an interview in his office on Friday.

“The mayor of Nago is opposed to Henoko and [the new governor] is opposed. For the U.S. and Japan, Okinawa used to be split on the base issue. But once Onaga is elected, we will be united.”

Inamine adamantly opposes the new base being constructed in his area, population 60,000, and has signaled that he will do everything in his power to stop the project.

He refused to allow port and road access to the construction site, forcing the central government to come up with a Plan B. Instead of building a conveyor belt to carry dirt into the landfill site, it now proposes bringing dirt in by truck along national roads, circumventing the need for the mayor’s approval.

Inamine said this plan would entail transporting 592 truckloads of dirt through the area each day for 182 days.

Local environmentalists say the massive land reclamation would endanger sea life, particularly the dugongs that live in the area.

“If Onaga [wins], it will show that Okinawa as a prefecture is completely against the idea of building new military bases here,” Inamine said.

Correction: An earlier version of this article referred to the endangered mammals in the Henoko area as manatees. They are more precisely dugongs, a distant relative of the manatee.