TOKYO, Japan -- Japan's ruling party picks its new leader Wednesday, with a mild-mannered former foreign minister and the Twitter-savvy vaccine chief leading the race to become the country's next prime minister.

The Liberal Democratic Party (LDP) is going to the polls with Prime Minister Yoshihide Suga opting not to stand, ending his tenure as premier after just a year in the role.

Whoever wins will be approved as prime minister by parliament within days, and will then contest general elections in which the LDP is expected to retain power.

The race to become the next leader of the world's third-largest economy is unusually tight this time around, in part because most of the party's powerful factions are not backing a candidate and their members will vote freely.

Four politicians are running, two men and two women, another unusual turn of events in a country that has never had a woman prime minister and has few prominent women political figures.

The race is expected to come down to former foreign minister Fumio Kishida, who lost out to Suga last year, and vaccine rollout chief Taro Kono, one of Japan's most recognizable politicians.

Hawkish right-winger Sanae Takaichi is reportedly a close third, while feminist former gender equality minister Seiko Noda has admitted she does not expect to advance beyond a first-round vote.

The initial vote on Wednesday afternoon will involve 382 LDP lawmakers and an equal number of rank-and-file party member votes.

But if no candidate secures a majority, the top two will advance to an immediate second round involving 382 lawmakers and one party representative from each of Japan's 47 regions.

Kono vs Kishida

Administrative reform minister Kono is the favorite with the public, reflecting in part his strong name recognition.

A former defense and foreign minister, he has been considered a likely candidate for the top job for years.

He favors a direct communication style that breaks from the cautious approach often preferred by Japanese politicians, and engages freely with the more than two million people who follow his Japanese Twitter account.

But he has also been described as abrasive and criticized for blocking people on Twitter and over allegations in tabloids that he bullied bureaucrats.

His main rival is Fumio Kishida, a former foreign minister and LDP policy chief who has pledged more pandemic stimulus if elected.

Kishida has sought to capitalise on public discontent over Suga's response to the pandemic, which has seen his government's approval ratings slump to record lows.

He has emphasized his skill as a listener and invited citizens to share their requests and proposals with him, even toting a suggestion box and notebook to scribble ideas at events.

The son of a Hiroshima family of politicians, Kishida unsuccessfully ran for the leadership against Suga last year, and said the experience had made him more forceful and determined.

Whoever wins the race will face a plethora of challenges, from driving a post-pandemic economic recovery to confronting threats from North Korea and China.