Tokyo (AFP) - Japan's ruling coalition headed by Prime Minister Shinzo Abe is set to sweep elections this weekend, retaining its unassailable two-thirds majority and crushing a divided and demoralised opposition, polls showed Thursday.

Abe's Liberal Democratic Party (LDP) and its junior partner Komeito will likely secure 317 of the 475 seats, giving them the super-majority they need in the powerful lower chamber to force through legislation, a poll published by the Asahi Shimbun newspaper said.

That would insulate the nationalist prime minister even if his coalition loses control of the upper house in an election expected in 2016.

The LDP is projected to win between 290 and 318 of the available seats, while Komeito could bag between 29 and 35, the Asahi poll showed.

Before last month's dissolution, the LDP held 295 seats and Komeito had 31.

The Democratic Party of Japan (DPJ), whose three years of disorganised government between 2009 and 2012 disappointed voters, will likely adorn its current parlous tally of 62 seats with a couple of dozen more but remain neutered.

Abe's gains are expected to come partly from the carcasses of now-defunct minor party groupings that have split in two or dissolved since his 2012 win.

However, the liberal-leaning Asahi noted, around 40 percent of voters have not decided how they will cast their ballots, and could -- theoretically at least -- change the results.

Observers expect a poor turnout at polling stations on Sunday, with many voters unenthusiastic about a general election just half way through the usual four-year term.

Despite growing disenchantment with Abe, whose "Abenomics" reforms are having an uneven effect, many voters feel there is no feasible alternative, leading some commentators to say the prime minister will win by default.