Japan's ruling Liberal Democratic Party(LDP) is set to elect its new leader on Monday, who is then widely expected to succeed Shinzo Abe as the country's new prime minister.

This comes after Abe announced he would step down over health reasons.

The LDP will convene on Monday a joint plenary meeting of party members from both houses of parliament, where 394 Diet members and 141 representatives from 47 prefectures will cast their ballots. 

Whoever wins the majority will become the new leader.

Out of three candidates - former Defense Minister Shigeru Ishiba, former Foreign Minister Fumio Kishida, and Chief Cabinet Secretary Yoshihide Suga - Suga is the most likely contender with backing from the party's major factions.

The LDP and main opposition Constitutional Democratic Party of Japan have agreed to convene an extraordinary Diet session and choose a new prime minister on Wednesday.

The new LDP president is all but certain to become Japan's prime minister as the party controls the lower house.