Four members of the Constitutional Democratic Party of Japan (CDP) filed their candidacies Saturday for the main opposition party's Sept. 23 leadership election.

The candidates are former Prime Minister Yoshihiko Noda, 67, former party leader Yukio Edano, 60, current chief Kenta Izumi, 50, and Lower House lawmaker Harumi Yoshida, 52.

Major topics in the race include cooperation with other opposition forces such as Nippon Ishin no Kai (Japan Innovation Party) and the Japanese Communist Party, 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.

At a joint news 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."

Edano said that the only and biggest mission was to "overcome political distrust and create a new option for government."

Izumi, meanwhile, referenced accomplishments during his three-year tenure as party leader.

"I have made advances with the aim to make the CDP capable of serving in government," he said, adding that he would oversee "a stable government."

Yoshida emphasized renewal, saying that she hoped to make politics "down-to-earth" and "not bound by convention."

Former CDP Executive Deputy President Kenji Eda, 68, who had also been exploring a bid, agreed at the last minute to back Yoshida.

The race comes as Izumi's current term expires at the end of this month. The new leader's term will run through the end of September 2027.