TOKYO • A surge in coronavirus cases in Japan has dealt a blow to Prime Minister Yoshihide Suga's once strong public support, raising the risk that he may be replaced by the ruling party ahead of an election that must be held by October.

Mr Suga enjoyed some of the highest approval ratings on record for a new prime minister last September, when the ruling Liberal Democratic Party (LDP) installed him as its leader.

But with poll numbers falling as sharply as Covid-19 cases rise, questions are emerging as to whether he might join the long list of Japanese premiers forced out after short stints.

"It's likely they will seek to vote in a more popular leader in the September party leadership election," said University of Tokyo political science professor Yu Uchiyama, adding that "a lot of LDP lawmakers" were concerned about their prospects under the Suga banner.

"The party leader is the face of the Lower House election," Prof Uchiyama added.

Support for Mr Suga's Cabinet tumbled 7 percentage points from the previous month to 33 per cent in a poll published by the Mainichi newspaper last Saturday, compared with 57 per cent of respondents who said they did not support the Cabinet.

Mr Suga is set to give a policy speech at the opening of the new parliamentary session today, in which he may lay out plans to add penalties to a law on virus management.

The session provides the Prime Minister with a chance to try to win back support for his government before a crucial decision is made on whether to go ahead and stage the Tokyo Olympics, an event set to start in July that he has said he is determined to hold despite mounting opposition.

Mr Suga, 72, came to power promising to maintain the ultra-easy monetary stance and other policies that helped make his predecessor, Mr Shinzo Abe, Japan's longest-serving prime minister.

At the same time, the farmer's son signalled greater focus than his long-time boss on pocket-book issues such as mobile phone charges. He laid out a dual strategy of bolstering the economy while containing the virus.

The continuity pledge helped send the Nikkei 225 Stock Average to an all-time high in dollar terms this month, even as the economy staggered back from the worst downturn on record.

But public opinion quickly began to sour after Mr Suga blocked a group of scholars who had been critical of Mr Abe's policies from an academic advisory body and a campaign finance probe entangled several of the former prime minister's top aides.

At the same, the government came under increasing criticism for maintaining its "Go-To" travel campaign to spur domestic spending despite concerns that it was helping to spread the virus.

Mr Suga resisted growing calls from regional leaders to declare a state of emergency - retreading a debate that drove down Mr Abe's popularity before he resigned due to the return of a chronic illness.

Mr Suga finally declared an emergency for the Tokyo region on Jan 7 after several record-breaking infection announcements, a move that about 80 per cent of respondents to a survey by public broadcaster NHK said was too late.

The expansion also strengthened the likelihood of the world's third-largest economy slipping back into reverse this quarter.

Mr Suga does not have much time to turn things around. Japanese law requires a Lower House election by October.

BLOOMBERG