TOKYO -- Japan's ruling Liberal Democratic Party (LDP) officially launched its leadership election campaign on Monday, with five candidates filing their candidacies.

The contenders are Agriculture Minister Shinjiro Koizumi, former Economic Security Ministers Takayuki Kobayashi and Sanae Takaichi, Chief Cabinet Secretary Yoshimasa Hayashi, and former LDP Secretary-General Toshimitsu Motegi.

All five also ran in last year's election, which saw a record nine candidates.

The contest will focus on issues such as cooperation with opposition parties, economic measures to tackle rising prices, and rebuilding the party after successive election defeats and political funding scandals.

Candidacy registration began at 10 a.m. local time at the LDP headquarters in Tokyo, where each candidate's representative submitted the required list of 20 recommending lawmakers.

The candidates will deliver their speeches on Monday afternoon at party headquarters, marking the official start of full-scale debate.

This year, over 910,000 party members will take part in voting, the national broadcaster NHK reported.

A total of 590 ballots will be cast, split evenly between Diet member votes (295) and party member votes (295). Ballots from party members will be finalized the day before lawmakers vote on Oct. 4, after which both sets will be counted together to decide the new party leader.

Japanese Prime Minister Shigeru Ishiba announced earlier this month that he will step down as the LDP head, triggering an early leadership contest within the party.

Once a new LDP president is chosen, the parliament will hold a prime ministerial designation vote.

Even though the ruling bloc has failed to secure a majority in both chambers of the parliament, the new LDP leader is highly likely to become the country's next prime minister since the LDP remains the largest party, analysts said.