Voting is underway in the Yokohama mayoral election, with the result set to have major implications for Prime Minister Yoshihide Suga's hopes of remaining in power beyond the fall.

Hachiro Okonogi, a former chairman of the National Public Safety Commission and a close Suga ally, and the opposition-backed Takeharu Yamanaka appeared to be neck-and-neck heading into the Sunday poll, with incumbent Mayor Fumiko Hayashi trailing.

A loss by Okonogi, 56, would be a significant blow to Suga heading into a leadership race of the ruling Liberal Democratic Party and a general election in the coming weeks and months.