Heavy snow hit large swathes of Japan on Saturday, the eve of a general election, fuelling speculation the ruling coalition is on course to an easy victory on low voter turnout.

It was already snowing heavily in large areas of the country along the coast of the Sea of Japan (East Sea) on Saturday, though Tokyo remained clear and sunny.

The weather agency warned of snowfall of as much as 80 centimetres (30 inches) in central and northern regions by the Sunday morning, when polls open.

The poor conditions could put off already unenthusiastic voters and push turnout to a record low for the elections, which were called two years ahead of schedule.

Early opinion polls have shown Prime Minister Shinzo Abe's coalition is likely to secure more than 300 of the 475 contested seats, giving them the super-majority they need in the powerful lower house to force through legislation.

The ruling coalition is made of Abe's conservative Liberal Democratic Party (LDP), supported by businesses and a network of campaign groups nationwide, as well as its junior partner Komeito which is backed by a big lay Buddhist group.

Their predicted victory is largely thanks to an unprepared and underwhelming opposition, political pundits have said.

A recent survey has found just two-thirds of voters expressed any interest in the vote, down from 80 percent ahead of the December 2012 election when Abe rose to power.

"Abe's expected victory is the result of the self-destruction of the opposition," Shinichi Nishikawa, professor of politics at Meiji University in Tokyo, told AFP earlier this week.

"For many voters, there is no alternative but the LDP," Nishikawa said.

Abe has billed Sunday's election as a referendum on his pro-spending growth policy.

His two years in power have been characterised by his bid to reinvigorate Japan's sagging economy with what he has called the "three arrows" of Abenomics -- monetary easing, fiscal stimulus and structural changes.

The first two arrows have largely hit their target -- the once-painfully high yen has plunged, sending stocks higher.

But the reform arrow remains in the quiver; critics say Abe has not been bold enough to take on the vested interests that are the real key to reversing nearly two decades of economic underperformance.

A new mandate from the electorate would give Abe a straight four years' run at some of the more difficult reforms.