Japan's former foreign minister, Fumio Kishida, has won the governing party leadership election and is set to become the next prime minister.

Kishida replaces outgoing party leader, Prime Minister Yoshihide Suga, who is stepping down after serving only one year since taking office last September.

As new leader of the Liberal Democratic Party, Kishida is certain to be elected the next prime minister on Monday in parliament, where his party and coalition partner control the house.

Kishida beat Taro Kono, the vaccinations minister, in a runoff after moving ahead of two female candidates, Sanae Takaichi and Seiko Noda, in the first round.

Kishida needs to change the party's high-handed reputation, worsened by the outgoing prime minister, Mr Suga, who angered the public over his handling of the coronavirus pandemic and insistence on holding the Olympics in Tokyo this past summer.

The long-ruling conservative Liberal Democratic Party desperately needs to quickly turn around plunging public support ahead of lower house elections coming within two months, observers say.

At a Tokyo hotel, lawmakers cast their votes one by one in a ballot box on stage when their names were called.

Kono, known as something of a maverick and a reformist, supports eventually phasing out nuclear energy, while Kishida calls for growth and distribution under his "new capitalism", saying Abe's economic policy only benefited big companies.

Takaichi, by far the most hawkish who wants greater military capability and spending, promised to visit the controversial Yasukuni Shrine. Noda pushed for women's rights and diversity.

Overall, little change is expected in key diplomatic and security policies under the new leader, said Yu Uchiyama, a political science professor at the University of Tokyo.

All of the candidates support close Japan-US security ties and partnerships with other like-minded democracies in Asia and Europe, in part to counter China's growing influence.

Analysts think Suga lost support because of party complacency and an increasingly high-handed approach forged during Shinzo Abe's long leadership.

The party vote could end an era of unusual political stability and return Japan to "revolving door" leadership.

"Concern is not about individuals but stability of Japanese politics," said Michael Green, senior vice president for Asia at the Center for Strategic and International Studies.

"It's about whether or not we are entering a period in Japanese politics of instability and short-term prime ministership," he said. "It makes it very hard to move forward on agenda."

Suga is leaving only a year after taking office as a pinch hitter for Abe, who suddenly resigned over health problems, ending his nearly eight-year leadership, the longest in Japan's constitutional history.