TOKYO: Japan's outgoing Prime Minister Yoshihide Suga will back the popular minister in charge of the nation's vaccination rollout, Taro Kono, to succeed him, Nippon News Network reported on Saturday.

Political manoeuvring was heating up among potential candidates and ruling party grandees on Saturday, a day after Suga's surprise announcement that he was stepping down, ending a one-year term as prime minister that has seen his support crumble as COVID-19 surged.

Hours after Suga's announcement, broadcaster TBS reported, without citing sources, that Kono intended to run for head of the Liberal Democratic Party (LDP). Kono told reporters only that he wanted to consult party colleagues before deciding.

Suga is expected to stay on until his successor is chosen in the party election scheduled for Sept. 29. The LDP leader will become prime minister given the party's majority in parliament.

A former foreign and defence minister, Kono, 58, is popular among young voters after building support through Twitter, where he has 2.3 million followers - a rarity in Japanese politics, which is dominated by older men less adept with social media.

Former foreign minister Fumio Kishida has already thrown his hat in the ring, while several others have voiced interest.

With no clear front-runner, the stance of Suga's predecessor Shinzo Abe will be closely watched, given his influence inside the two largest factions of the LDP and among conservative MPs, analysts say.

Abe, who stepped down citing ill health last September after a record eight-year term, had publicly backed Suga's reelection. With Suga out, Abe now supports former internal affairs minister Sanae Takaichi, who is close to the former premier, TBS said.

Takaichi, who would be Japan's first female prime minister, had been seen as struggling to gain the backing of the 20 LDP lawmakers needed to run in the party race. Abe's support could boost her chances.

Kishida said on Saturday he would leave the national sales tax at 10% if elected, reiterating that he would fund a new economic package worth tens of trillions of yen (hundreds of billions of dollars) by issuing more government bonds.

"I'm not thinking of touching the sales tax for the time being," Kishida told a Nippon News Network programme. "We then must consider Japan's finances from the standpoint of how to make use of the fruit of economic growth."

Before Abe, Japan had six prime ministers in as many years.