TOKYO - An official campaigning for the leadership election of Japan's largest opposition party began on Saturday, with four contenders debating on how to work with other parties in a general election expected later in the year and bring about a change in government, local media reported.

Four members of the Constitutional Democratic Party (CDP) of Japan, including a former prime minister and two lawmakers with experience running the party, filed candidacies on the day for the Sept 23 election, Kyodo News reported.

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Familiar faces vying for the leadership are Yoshihiko Noda, 67, who served as Japan's prime minister from 2011 to 2012 under the now-defunct Democratic Party of Japan, Yukio Edano, 60, leader of the CDP from its 2017 founding to 2021, and his successor, incumbent head Kenta Izumi, 50.

First-term House of Representatives lawmaker Harumi Yoshida, 52, was the final addition to the roster and is the only woman running.

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The 17-day campaign is expected to focus on how to cooperate with other opposition forces as a snap general election is expected to take place as early as this autumn. The CDP is aiming to take power from the ruling bloc led by the Liberal Democratic Party, the report said.

At a joint press conference by the four candidates at party headquarters, Noda said that the race was a "leadership election on the eve of a change of government, in which we will align our thoughts and efforts to seize power."