Japanese Economy, Trade and Industry Minister Yuko Obuchi bows her head as she resigns her post at a press conference at her office in Tokyo on Monday. Obuchi resigned over claims that she misused political funds, including buying both votes and makeup, dealing a blow to Prime Minister Shinzo Abe's gender reform drive. Photo: AFP

Two Japanese cabinet ministers resigned on Monday, dealing Prime Minister Shinzo Abe his biggest setback since he took office in December 2012.

The resignations of the two women could complicate tough decisions on key policies, including whether to go ahead with an unpopular plan to raise the sales tax and planned restarts of nuclear reactors shut down after the 2011 Fukushima disaster.

Abe hopes to contain the damage through swift replacements of the two, but the opposition is looking for other potentially vulnerable ministers also appointed in an early September cabinet reshuffle. Further resignations could raise doubts about Abe's own future, some political experts said.

"There are more than two (other) ministers with regard to whom there are suspicions," Yukio Edano, the opposition Democratic Party's second-in-command, told reporters. "We will coordinate our actions among opposition parties, point out the problems and ask for explanations about the other ministers."

He did not identify the ministers nor explain how the opposition planned to seek any explanations.

Trade and Industry Minister Yuko Obuchi, 40, the daughter of a prime minister and tipped as a future contender to become Japan's first female premier, tendered her resignation after allegations that her support groups misused political funds.

Just hours later, Justice Minister Midori Matsushima also resigned.

The opposition Democratic Party had filed a criminal complaint against Matsushima, accusing her of violating the election law by distributing paper fans to voters.

Obuchi and Matsushima were two of five women appointed by Abe in the cabinet reshuffle, a move intended to boost his popularity and show his commitment to promoting women as part of his "Abenomics" strategy to revive the economy.

"I appointed them and as prime minister, I bear responsibility," Abe told reporters at his office. "I deeply apologize to the people of the nation." Abe added he wanted to pick successors for the two posts within the day.

As head of the powerful Ministry of Economy, Trade and Industry (METI), Obuchi was tasked with selling Abe's unpopular plan to restart nuclear reactors to a wary public worried about safety. The process to restart the reactors is made difficult but unlikely to be delayed by her resignation, officials said.

"We cannot let economic policy and energy policy stagnate at METI because of my problems, so I will resign my position," a solemn Obuchi told a nationally televised news conference, bowing deeply in apology.

The departures are the first cabinet resignations for Abe, who took office in December 2012 for a rare second term.

"They are trying to limit the damage by getting rid of those (two) quickly," said Tomoaki Iwai, a political science professor at Nihon University.

"But Abe's support will decline and ... policy implementation will not go smoothly," he said, adding the situation would become far tougher if other ministers also quit.

Abe has decided to appoint Yoichi Miyazawa as trade minister to replace Obuchi, reported Japan's NHK.

Abe also decided to name Yoko Kamikawa as the new justice minister.