TOKYO: Japanese voters strongly support Taro Kono, minister in charge of fighting COVID-19, as the next prime minister according to a second opinion poll, as potential candidates prepare to join what has become a wide-open contest for ruling party leader.

Prime Minister Yoshihide Suga's shock Friday announcement he was stepping down has thrown a ruling Liberal Democratic Party (LDP) leadership race set for Sept 29 into disarray, with a wide array of candidates set to vie for the top job.

The LDP's majority in parliament guarantees the winner will become prime minister.

According to the survey by the Yomiuri Shimbun daily published on Monday, 23% of respondents said Kono, the minister in charge of vaccines, was the most suitable person to take over - echoing a Sunday poll that had 31.9% favouring Kono.

Kono held a narrow edge over former defence minister Shigeru Ishiba, with 21%. Former foreign minister Fumio Kishida, who has already formally announced his candidacy, trailed with 12%.

A former foreign and defence minister, the 58-year-old Kono, educated at Georgetown University and a fluent English speaker, has built a popular following among young voters with an active social media presence in two languages and 2.3 million followers on his Japanese page alone.

Kono has long been a favoured candidate among voters for prime minister and has made no secret of wanting the job, but party elders are wary of him for his outspokenness and reputation as a maverick. Others feel he is still too young for the job.

Over the weekend, though, one TV network reported that Kono had gained Suga's backing.

Former defence minister Ishiba, 64, has had strong support among rank-and-file party members in the past, defeating Suga's predecessor Shinzo Abe in the first round of a 2012 leadership race. He lost in a later round, when only lawmakers could vote, and has since lost two more leadership contests.

Kishida, also 64, was seen as likely heir last year when Abe quit due to illness, but his low-key, soft-spoken style typically lands him low in voter surveys. He has called for reducing income disparities and pledged support for the economically vulnerable.

Unlike last year's leadership race, when Suga emerged the winner, this time ordinary party members at the prefectural level will also be able to vote, which could make the outcome harder to predict.

Potential candidates spent a busy weekend meeting with other lawmakers, sounding them out for support, media said. Each needs to gather 20 supporters by Sept 17 to become a formal candidate, with the vote on Sept 29.

Should the results be close, a second round would be held with only lawmakers allowed to vote. The winner will choose when to call a general election, likely to come anywhere from Oct 17 to as late as Nov 28.

Abe's actions are being closely watched for signs of whom he will support. Japan's longest-serving prime minister still retains influence in the party's two largest factions and among conservative lawmakers.

Japanese media has reported that Abe will be backing former internal affairs minister Sanae Takaichi, who hopes to become Japan's first woman prime minister.

But Monday's Yomiuri survey had Takaichi trailing badly at 3% - just behind Abe himself, at 5%.