Japanese prime minister Shigeru Ishiba's conservative ruling party braced for a blow to its comfortable majority in the lower house of parliament in Sunday’s elections amid public rage over the party’s financial scandals and discontent over a stagnant economy.

The results could weaken Ishiba's grip on power, possibly leading Japan into political uncertainty, though a change of government was not expected.

Ishiba took office on October 1, replacing his predecessor Fumio Kishida who resigned after failing to pacify the public over widespread slush fund practices among Liberal Democratic Party lawmakers.

Ishiba immediately ordered a snap election in hopes of shoring up support by using his outspoken, reformist image.

Voting began Sunday morning across Japan, where 1,344 candidates, including a record 314 women, are running for office.

Polls close at 8pm (local time, 12am NZ time), with early results expected within hours.

Ishiba has set a goal of retaining 233 seats for the ruling coalition between the LDP and its Buddhist-backed junior partner Komeito, a majority in the 465-member lower house, the more powerful of Japan’s two-chamber parliament.

Ishiba, in his final speeches Saturday in Tokyo, apologised over his party’s mishandling of funds and pledged “to restart as an equal, fair, humble and honest party.”

He said only the LDP’s ruling coalition can responsibly run Japan with its experience and dependable policies. Once a popular politician known for his criticism of even his own party's policies, Ishiba has also seen support for his weeks-old Cabinet plunge.

The biggest opposition party, the Constitutional Democratic Party of Japan, is led by centrist leader Yoshihiko Noda who briefly served as prime minister during the LDP’s 2009-2012 descent from power.

Noda's party is expected to make significant gains. Noda says Sunday’s election is a rare chance for a change of government, which will be the most effective political reform, though his party has trouble finding other opposition groups with which to cooperate.

At a downtown Tokyo polling station early Sunday, a number of voters said they considered the corruption scandal and economic measures.

A 77-year-old man said his biggest concern was rising prices and wondered if the LDP should win despite the wrongdoings.

Another resident in her 60s said she would vote in hope of making a change.

Analysts suggest Ishiba could fall short of reaching his target, though his LDP was expected to remain the top party in Japan’s parliament as voters are sceptical about the opposition's ability and inexperience.

Losing a majority would mean Ishiba would have difficulty establishing policies and could face calls from within his party for a replacement ahead of next summer’s election in the upper house, experts say.

“The public’s criticisms against the slush funds scandal has intensified, and it won’t go away easily,” said Izuru Makihara, a University of Tokyo professor of politics and public policy.

“There is a growing sense of fairness and people are rejecting privileges for politicians.”

Makihara suggested Ishiba needs bold political reform measures to regain public trust.

Ishiba pledged to revitalise the rural economy, address Japan’s falling birth rate and bolster defence. But his Cabinet has old faces, only two women and was seen as alienating members of the scandal-tainted faction led by late premier Shinzo Abe.

Ishiba quickly retreated from earlier support for a dual surname option for married couples and legalizing same-sex marriage, an apparent compromise to the party’s influential ultra-conservatives.

His popularity fell because of “the gap in what the public expected him to be as prime minister versus the reality of what he brought as prime minister,” said Rintaro Nishimura, a political analyst at The Asia Group.

The LDP is also being tested Sunday for its ability to break from the legacy of Abe, whose policies focused on security, trade and industry but largely ignored equality and diversity, and its nearly eight-year long rule led to the corruption, experts say.

There could be regrouping attempts among opposition parties to decide whether to cooperate among themselves or join the ruling coalition, political watchers say.

Potential new partners for the LDP include the Democratic Party of the People, a breakaway group from the CPDJ, which calls for lower taxes, and a conservative Japan Innovation Party, though both are currently denying a possible coalition with the LDP.

The LDP, whose dissolution of most factions that used to help bring together support for pushing through on elections and on policy, is less cohesive and could enter the era of short-lived prime ministers. Ishiba is expected to last at least until the ruling bloc approves key budget plans at the end of December.