Japan's top government spokesman, Yoshihide Suga, has emerged as a strong contender as the head of government after securing the backing of a large section of the ruling party to become the next prime minister.

According to the Japanese public broadcaster NHK, Suga is in good position to replace Prime Minister Shinzo Abe, who last week announced he would step down owing to an illness.

Japan's chief cabinet secretary and a long-time lieutenant of the outgoing Prime Minister, Suga is widely expected to stay the policy course set out by Abe, including the "Abenomics" strategy aimed at reviving the economy and keeping it afloat amid the COVID-19 pandemic.

Suga has not publicly announced his candidacy for leader of the Liberal Democratic Party (LDP). Media reported he would formally announce his intention to run on Wednesday, according to CGTN.

The party's leader will almost certainly become prime minister because of its majority in the lower house of parliament. The new leader will replace Abe, who abruptly announced on Friday he was stepping down for health reasons.

In a meeting on Tuesday to decide on the format of the election, LDP executives agreed to a simplified vote by party MPs from both chambers of parliament and heads of local chapters, party Secretary-General Toshihiro Nikai said.

The proposal to exclude votes by rank-and-file members favors Suga, who has now reportedly locked in support from the party's biggest factions.

"We must elect a new leader as soon as possible to avoid creating a political vacuum," Nikai told reporters. "There was no objection to my view at the meeting."

The LDP is expected to hold its leadership vote on September 14.

Another contender for the post is Fumio Kishida, a former foreign minister. Current Foreign Minister Toshimitsu Motegi and Defense Minister Taro Kono both said on Tuesday they had not yet decided whether to run.

The reported backing of the LDP's biggest Hosoda faction for Suga follows media reports of support from the powerful faction led by Deputy Prime Minister Taro Aso. LDP heavyweight Nikai is also supporting Suga.