Japan's Prime Minister Shinzo Abe suffered a double setback Monday with the resignations of two female cabinet ministers over claims they misused political funds, dealing a blow to his proclaimed gender reform drive.

Industry minister Yuko Obuchi and Midori Matsushima, justice minister, fell on their swords after days of allegations that they had misspent money in what opponents insisted was an attempt to buy votes.

Their loss reduces to three the number of women in the cabinet, after Abe's widely-praised move in September to promote a record-tying five to his administration.

"I'm the person who appointed the two. As prime minister, I take responsibility for this and deeply apologise for this situation," Abe told reporters, adding he would replace them both within the day.

The double resignations are the first significant problem for Abe since he swept to power in December 2012, ending years of fragile governments that swapped prime ministers on an annual basis.

While commentators generally agreed that this would not be the end of the hard-charging premier, who has set his sights on reinvigorating Japan's lacklustre economy, they cautioned that he was now vulnerable.

"This is Abe's first major stumble," said Tomoaki Iwai, professor of politics at Nihon University in Tokyo.

"Because of the double resignations, his approval rate is likely to fall and Abe will be under pressure," Iwai said. "If he repeats similar mistakes, it's going to be a fatal blow to his administration."

Obuchi, who inherited the dynasty of her father, a former prime minister, offered a fresh, youthful face on the front benches -- a place generally dominated by older men.

As a mother of two, her family-friendly image was expected to help smooth the way to re-starting Japan's stalled nuclear power plants, with supporters hoping she could convince a sceptical public of their safety.

But her elevation had also reportedly irked male politicians who felt they had loyally served their time on the backbenches and had been passed over in favour of a young woman with little cabinet experience.

Subsidised theatre trips

She began to come unstuck last week when reports emerged that she had spent political funds on make-up and accessories as gifts for supporters.

They were followed by claims that she had subsidised theatre trips for voters from her rural constituency.

The claims, which were priced at tens of millions of yen (hundreds of thousands of dollars) over several years, were taken as evidence of attempted vote buying.

"It is not permissible for me as Minister of Economy, Trade and Industry to have economy and energy policies stalled because of my own problems," she told a press conference carried live on multiple television channels.

"I will resign and focus on probing what has been called into question," she told reporters after a 30-minute meeting with Abe.

Matsushima has been under fire for allegedly giving out cheap fans with her name and picture printed on them -- another example, said detractors, of trying to buy support.

One of those fans was for sale on an Internet auction site Monday, with the price having reached 2,100 yen ($20).

Money scandals are not uncommon in Japanese politics, where the pork barrel reigns and rules on spending tend to be slightly opaque, barring little except explicit bribery and vote buying.

The promotion of five women to the cabinet was seen as part of Abe's bid to boost the role of women in society, a move viewed as vital to help plug the holes in Japan's workforce and make better use of a pool of latent talent.

Asked if she felt her relative youth and her gender had played a role in the way the scandal emerged, Obuchi demurred.

"I only learnt now that this issue could be seen in this light," she said.

Sadakazu Tanigaki, secretary-general and the number two in Abe's ruling Liberal Democratic Party, earlier said Obuchi's resignation was "extremely regrettable."

"As Ms Obuchi was symbolic of women's having an active role, I think there will be damage (to the government)," Tanigaki told reporters.