Vote-counting began Sunday evening at 85 locations in Chiba Prefecture to pick a successor to outgoing Gov. Takeshi Numata.
Results of the Chiba gubernatorial race -- viewed as a prelude to the July House of Councilors election -- were expected to be known late Sunday night.
Among five candidates, all newcomers, vying for the post are two former Upper House members, Ryozo Iwase, 67, and Akiko Domoto, 68.
The three other candidates are Masanori Kadota, 53, of the Funabashi municipal assembly in the prefecture, 55-year-old urban planner Yasuhiko Wakai, and 50-year-old doctor Izumi Kono.
Iwase, a former head of the prefecture's education board, is supported by the ruling Liberal Democratic Party, the New Conservative Party and the Liberal League, while Kono is backed by the Japanese Communist Party.
The opposition Democratic Party of Japan and the Social Democratic Party are endorsing Wakai, while Domoto, unaffiliated with any political party, is supported by groups concerned with women's issues.
The LDP's key ally, New Komeito, is backing no candidate.
The result of Sunday's race will also likely affect the upcoming LDP presidential election, for which Junichiro Koizumi and Hiromu Nonaka, former secretary general, are emerging as possible candidates.
If the LDP-supported Iwase wins the race, it will likely boost calls for Nonaka, who has closer ties with New Komeito, a key coalition partner, party sources said.
Should he lose badly, there will be more calls for the reform-minded Koizumi, they said.