TOKYO - Japan's ruling and opposition parties on Friday agreed to elect a new prime minister to replace Shigeru Ishiba on Oct 21, local media reported.

The ruling Liberal Democratic Party (LDP) and the main opposition Constitutional Democratic Party of Japan agreed to hold the parliamentary vote to pick the successor to outgoing Ishiba on Oct 21, the day when an extraordinary Diet session kicks off, Kyodo News reported.

The two parties also confirmed that the term of the upcoming Diet session will be 58 days, ending on Dec 17.

Sanae Takaichi won the LDP presidential election on Oct 4. For the leader of the ruling party to become the next prime minister, they must be appointed by the Diet, Japan's parliament.

Both houses of the Diet vote to choose the prime minister, but if they make different choices, the powerful lower house's pick prevails. A candidate who wins a majority in the first round is named prime minister. If no one secures a majority, a runoff vote is held between the top two vote-getters, and the one with more votes is chosen even without a majority.

Jiji Press reported that if Takaichi is elected prime minister, she will immediately formulate economic measures to deal with rising prices and other issues and is expected to submit a supplementary budget bill to the parliament for review in early December.