“The political status quo has continued while politics itself has lost the public’s confidence,” said the 65-year-old.

Pensioner Sumiko Sakai

Abe cut a contrasting figure by kicking off his offensive in the bucolic farming country of Fukushima, signalling his commitment to rebuilding the region that was hit hard by the 2011 nuclear power plant meltdown.

He pledged a major expansion of social programmes, including offering free early childhood education in a bid to get more women into work, while also talking tough on North Korea.

In an obvious dig at Koike, he urged voters to consider his policies, rather than catchy sound bites.

“Slogans do not open the way to the future. Policies unlock the future. We must not lose,” he said.

The 12-day campaign will be fought around reviving Japan’s once world-beating economy and the ever-present threat of North Korea, which has threatened to “sink” the country into the sea.

Koike’s Party of Hope has swallowed up and replaced most of the main opposition party in the space of a week, transforming Japan’s staid political landscape.

But surveys suggest her bandwagon is grinding to a halt as she herself refuses to run for prime minister, focusing instead on governing the world’s most populous city which will host the Olympic Games in just three years.

A poll in the Yomiuri daily suggested 32 per cent of voters plan to vote for Abe’s conservative LDP with 13 per cent for the Party of Hope – down six percentage points from the previous poll in late September.

On the streets of Tokyo, Abe’s message that the election is about the coming generations appeared to resonate.

“At my age, what interests me is the future of my children and my grandchildren. We need to prepare a better world for them,” said 76-year-old pensioner Sumiko Sakai.

Abe is seeking a fresh term at the helm of the Asian economic powerhouse and key US regional ally. He unexpectedly called the snap election to capitalise on a weak and fractured opposition.

But Koike stole his limelight by launching her party, attacking Abe’s government for being too slow to reform the country, which is weighed down by an ageing population, deflation and a huge debt.

Abe’s trademark “Abenomics” policy – a vow to kick deflation and achieve 2 per cent inflation with stable growth – has largely fallen flat.

Critics argue that Abe called the early election to divert attention from a string of scandals, including allegations of favouritism to a friend in a business deal – which the premier strongly denies.

And analysts say the October 22 vote is effectively a referendum on Abe, who has enjoyed unrivalled political strength for the past five years in part because of a lack of credible opposition, while his key policies remained controversial or unpopular.

For her part, Koike says her new group promotes “compassionate conservatism” and hopes to distinguish herself from Abe by pledging a phase-out of nuclear power by 2030 and a freeze on a planned sales tax increase.

Koike sceptics have said she simply repeats vague, catchy phrases and lacks details, such as how she plans to pay for her ambitious projects.

More than 1,000 candidates were expected to run for 465 seats in the all-powerful lower house – a reduction of 10 seats from the previous election.

The outcome could create two rival conservative blocs with broadly similar diplomatic and defence policies, with fragmented leftist forces filling the gap, pundits say.

Before the campaign kicked off, Abe’s ruling bloc held a two-thirds majority, with his LDP holding 287 seats while its junior partner Komeito has 35.

Abe has said he would step down if his coalition fails to win a simple majority, but few analysts see that as a likely scenario, especially as Koike’s party is only putting up 235 candidates.