Voters handed Prime Minister Shinzo Abe a thumping victory in upper house elections Sunday, exit polls showed, likely ushering in a new period of stability for politically volatile Japan.

The projected victory means both chambers will be under government control, unblocking the bottleneck that has hampered legislation for the last six short-term premiers.

That will strengthen Abe's hand as he tries to push through painful, but necessary, structural reforms aimed at dragging Japan out of two decades of economic malaise.

"We want to respond to people's desire to feel a sense of economic improvement," Abe told reporters as the results emerged.

"I want to make a virtuous cycle of improving the employment situation, increasing salaries and bringing about a rise in corporate investment."

Exit polls by NHK showed Abe's Liberal Democratic Party and its junior partner New Komeito claimed at least 73 of the 121 seats being contested.

Voter turnout was low, at an estimated 52.60 percent, according to projections by Kyodo News.

There are 242 legislators in the upper house, serving six-year terms. Elections are held for half of the seats every three years. The coalition already has 59 seats that were not up for election on Sunday.

Since romping to power in December's vote for the more powerful lower house, the hard-charging Abe has unleashed a wave of spending and pressured the central bank to flood the market with easy money.

The moves -- the first two "arrows" of a project dubbed "Abenomics" -- sent the yen plunging, to the delight of exporters, and the stock market soaring.

This, coupled with some feel-good figures on GDP growth, powered 60-percent-plus public approval ratings for the prime minister, whose disastrous first turn in the top job, till September 2007, has paled in the public mind.

The third arrow of Abe's policy programme remains hazy, but will include corporate tax breaks, special business zones, plans to boost the number of women in the workplace and Japan's participation in a mooted free trade area that encircles the Pacific.

However, observers say reforms will be tough. Superannuated farmers tending tiny plots make up a powerful lobby group that has already made clear its unease about the extra competition this Trans-Pacific Partnership (TPP) would bring.

The fact that these rural voters also form the backbone of support for the LDP could prove a problem for the premier.

Pundits say a big public endorsement protects him from the powerful vested interests inside the party that will agitate against the structural changes which economists agree the country badly needs.

LDP secretary general Shigeru Ishiba vowed Sunday the government would not be distracted from reforms, including on the TPP.

"Our party has a tradition of each member observing what has been decided," Ishiba said.

"We won an overwhelming victory after we made clear about our policy on the TPP."

Another issue for Abe is that the vast spending unleashed so far is worsening Japan's already eye-watering levels of debt. A slated increase in consumption tax to slow this rise risks dampening spending and irritating voters.

Japan's disheartened opposition barely put up a fight in the election. The main opposition party, the Democratic Party of Japan, is in disarray after three years of confused governance were capped with a drubbing in December's poll.

They and other smaller parties had united around one thing -- the need for Japan to graduate from nuclear power generation, a popular stance in a country badly scarred by the 2011 disaster at Fukushima.

But even Abe's pro-nuclear stance, and his vow to switch Japan's 48 mothballed reactors back on when they have passed rigorous new safety checks, was not enough to dampen enthusiasm for his economic trump card.

Abe's detractors fear Abenomics is a Trojan Horse aimed at securing the hawkish premier enough power to implement his conservative social agenda.

They fear this will mean a loosening of Japan's constitutional commitment to pacifism, a boosting of the military and a more strident tone in already-strained relations with China and South Korea, both of whom have territorial disputes with Tokyo.

"Let's revise the constitution in order to create a proud country," the hawkish leader told voters on the eve of Sunday's poll.

Official results will likely come Monday.