Four cabinet ministers in Japan quit on Thursday over a fundraising scandal involving the ruling party's most powerful faction.
More than 500m yen (£2.8m; $3.4m) is alleged to have ended up in slush funds over a five-year period through 2022.
Tokyo prosecutors have also launched a corruption probe, Nikkei reported.
It is the latest blow to Japan Prime Minister Fumio Kishida's increasingly unpopular government, whose approval ratings have plunged.
Public support for the ruling Liberal Democratic Party (LDP), which has been in power almost continuously since 1955, fell below 30% for the first time since 2012, an NHK survey on Tuesday showed.
Voters have been angered by inflation, as well as Mr Kishida's handling of earlier scandals.
Chief Cabinet Secretary and top government spokesman Hirokazu Matsuno, often seen as Mr Kishida's right-hand man and the face of his government, was the most prominent of the four ministers. Economy and Industry Minister Yasutoshi Nishimura, Internal Affairs Minister Junji Suzuki and Agriculture Minister Ichiro Miyashita also stepped down on Thursday.
Their replacements are expected to be announced by the end of the day.
In addition, five senior vice ministers and a parliamentary vice minister from the same faction, formerly led by the late PM Shinzo Abe, also quit.
The mass resignations now leave the LDP in the unusual situation of having no representatives from its largest and most powerful faction within the cabinet.
Mr Kishida, who took office in October 2021, said on Wednesday that he would deal with the allegations "head-on".
The faction allegedly failed to report hundreds of millions of yen in fundraising income.
Also known as the Seiwa policy group, the faction had set quotas for its members on the sale of tickets for party fundraising events.
When their sales exceeded the quotas, members received the additional funds. In and of itself, this does not violate Japanese law.
However, the allegations in the present case - which were triggered by a criminal complaint - suggest that the additional revenue was kept off the books and instead went into slush funds.
Mr Matsuno is himself accused of failing to report more than 10m yen in income.
Other major factions within the LDP, including one previously led by Mr Kishida, are also facing allegations of under-reporting fundraising income.
On Wednesday, the Lower House of Japan's Diet rejected a no-confidence motion filed by the opposition against Mr Kishida's cabinet.
The LDP is due to hold leadership elections next September. A general election is due in 2025.
Some observers have said that even if Mr Kishida can continue to hold on to his post, his credibility will be greatly dented by the ongoing scandal.
"Kishida will remain in power for now as there are no obvious other candidates for the next president. But if a strong contender emerges, there may be a move to drop Kishida," Yu Uchiyama, a professor of political science at the University of Tokyo, told Reuters this week.
