TOKYO, Sept 22, 2025 (BSS/AFP) - The leadership contest for Japan's ruling party kicked off on Monday, with five candidates vying to become the country's fourth prime minister in as many years.

Prime Minister Shigeru Ishiba threw in the towel on September 7 after a string of poor election results for the long-dominant but ailing Liberal Democratic Party (LDP).

Of the five contenders who filed their papers on Monday ahead of an October 4 party vote, Sanae Takaichi and Shinjiro Koizumi are the favourites, polls suggest.

Takaichi, 64, who would be Japan's first woman premier, is seen as a hard-line nationalist while Agriculture Minister Koizumi, 44, is the telegenic son of an ex-premier.

The others are Toshimitsu Motegi, 69, a former top diplomat with a reputation as a tough trade negotiator; Yoshimasa Hayashi, 64, the top government spokesman in Ishiba's cabinet with large ministerial experience; and former economic security minister Takayuki Kobayashi, 50.

The candidates will be formally approved before each of them gives a policy speech at LDP headquarters on Monday, election committee head Ichiro Aisawa said.

The LDP has governed Japan for all but four years since it was launched in 1955.

Whoever wins will face a host of complex issues including a rapidly ageing population, colossal national debt and a faltering economy plagued by rising prices.

The election on October 4 will be open to ordinary members of the LDP.

The head of the party usually becomes prime minister because of the party's long-held legislative majority with coalition partner Komeito.

But the coalition over the past year lost its majority in the both houses of parliament after two major election losses under Ishiba.