Japanese Prime Minister Shinzo Abe's ruling coalition on Sunday won local elections seen as a referendum on his efforts to boost the economy before upper house elections next year, news reports said.

Candidates backed by Abe's Liberal Democratic Party (LDP) and junior coalition partner Komeito were elected in all of the 10 gubernatorial polls held on Sunday across the nation, according to public broadcaster NHK and other reports.

Other polls to elect five mayors as well as local assembly members were also held nationwide in the first set of two rounds of local elections. The second set will be held on April 26.

"It was a great achievement," Toshimitsu Motegi, chief of the LDP's election bureau, told reporters after exit polls indicating the coalition victory were released by local media.

Motegi, a senior LDP lawmaker, said the triumph was largely due to voters' high expectations of efforts made by the ruling coalition to revive local economies.

Abe's LDP saw the local polls as a way of evaluating his drive to resuscitate Japan's economic fortunes, dubbed "Abenomics".

The efforts include massive government spending, monetary easing and an overhaul of the highly regulated economy.

The scheme kicked off a sharp decline in the yen and a stock market rally, but efforts to drag the country out of years of deflation have met with mixed success.

"The impact of Abenomics has finally emerged," LDP secretary-general Sadakazu Tanigaki told voters earlier in the northern city of Sapporo.

"The theme of these local elections is to capitalise on the impact across the nation," said Tanigaki, the ruling party's number two after Abe.

The main opposition Democratic Party of Japan (DPJ) also saw the local polls as a precursor to next year's upper house elections.

"It is very important for us to win seats... when we consider the next national election," DPJ president Katsuya Okada told reporters earlier.

The victorious coalition-backed candidates included two pro-nuclear politicians. They won gubernatorial polls in Fukui and Shimane in central and western Japan respectively, both of which host nuclear power plants.

The once nuclear-dependent country is now sceptical of the technology, with voters badly scarred by the disaster at Fukushima, where reactors went into meltdown after their cooling systems were swamped by a tsunami in 2011.

Japan's entire stable of nuclear power stations were gradually switched off following the disaster, while tens of thousands of people were evacuated because of rising levels of radiation. Many are still unable to return to their homes.

However, the country's nuclear watchdog has given the green light to restarting reactors. The pro-nuclear Abe and much of the industry are keen to return to atomic generation, largely because a plunging yen has sent the cost of dollar-denominated fossil fuels soaring.