TOKYO: Japan's ruling party faced mounting scrutiny on Thursday amid reports that lawmakers will be investigated over fundraising - a scandal that threatens to further dent Prime Minister Fumio Kishida's sinking popularity.

Tokyo prosecutors will start investigating several dozen lawmakers from the Liberal Democratic Party (LDP), including current ministers, next week over more than 100 million yen ($680,000) of fundraising proceeds that are not in official records, local media reported.

The investigation centres around money raised from ticket sales to party events - some of which was then given directly to lawmakers by the party and left off the books, according to the reports.

A spokesperson at the Tokyo Public Prosecutors Office said they were unable to answer questions on matters currently under investigation.

Kishida on Wednesday ordered his party to put a temporary halt to all such events and said he was tackling the issue "with a strong sense of crisis".

But the popularity of Kishida's administration has sunk to less than 30% in recent polls, due in part to voter worries over rising costs and looming tax hikes, and some analysts say Kishida may struggle to stay on even if a fractured opposition poses no immediate threat to his party's grip on power.

"I don't think he can hold on to power for that much longer...and that is in part because this scandal is big and we haven't seen the end of it yet," said Koichi Nakano, a professor specialising in Japanese politics at Tokyo's Sophia University.

The LDP - which has held power for nearly all of Japan's post-war era - is due to hold leadership elections in September with a general election due by October 2025 at the latest.

The probe focuses on funds raised by the biggest faction in the LDP which was once led by former Prime Minister Shinzo Abe, and both Trade Minister Yasutoshi Nishimura and Chief Cabinet Secretary Hirokazu Matsuno had overseen the faction's bookkeeping in the past five years, according to the Yomiuri newspaper.

Matsuno, who holds daily press conferences, has declined to comment on the allegations despite multiple questions from the media including on Thursday. Nishimura has also declined comment.

The LDP's secretary general, Toshimitsu Motegi, said this week that party leaders have been told to scrutinise their funding reports and make corrections if necessary.

Prosecutors plan to begin questioning lawmakers after the current session of parliament session ends on Dec. 13, the Yomiuri said.