Lawmakers from the main ruling Liberal Democratic Party are voting for their next leader. The winner is virtually assured to become Prime Minister.
They will choose between four political veterans: Regulatory Reform Minister Kono Taro, former LDP Policy Research Council Chairperson Kishida Fumio, former Internal Affairs and Communications Minister Takaichi Sanae, and LDP Executive Acting Secretary-General Noda Seiko.
382 LDP lawmakers are each eligible to cast a ballot.
Another 382 come from rank-and-file members, who have already voted. Their votes will be distributed according to proportional representation.
If no one wins more than half the votes, the top two candidates will compete in a runoff.
The Diet is expected to make the winner prime minister next Monday. A new Cabinet will then set the date for a Lower House election, which must be held within weeks.