TOKYO (AFP) - Tokyo voters headed to the polls on Sunday in a day seen as a litmus test ahead of national elections that could give Prime Minister Shinzo Abe an uninterrupted three years without a public vote.

Abe's Liberal Democratic Party, in partnership with the junior New Komeito, are expected to claim a comfortable majority in the 127-seat Tokyo Metropolitan Assembly.

The ballot is widely being seen as an indicator of public opinion in the run up to upper house polls expected on July 21.

It will be the first voters' verdict on Abe's administration, which came to power in December and still enjoys approval ratings of more than 60 per cent.

An economic policy blitz dubbed "Abenomics", which blends massive monetary easing, big fiscal spending and a series of reforms aimed at freeing up businesses, has dominated the opening months of the Abe government.

Japan's sleep-walking economy - the world's third largest - has been given a jolt by the moves, with the yen shedding some of its export-sapping strength and the stock market putting in the best performance in the developed world this year.

Despite a few weeks of wobbles that have seen the headline Nikkei 225 index loose some of its steam, many economists still feel Abenomics has legs.

If Mr Abe can secure control of the upper house in the July polls, it will relieve a legislative bottleneck and give him free rein to push through the painful reforms commentators say Japan desperately needs.

Detractors warn that with a majority in both houses, Abe will take his eye off the economic ball and push the conservative social agenda he was known for before the election, including a possible reassessment of Japan's wartime history.

They say this risks further irritating already inflamed relationships with China and South Korea.

The campaign in the Japanese capital has been relatively low key, with few issues of contention for Tokyo voters.

That is expected to mean a low turnout, giving a further boost to the establishment LDP, who have a solid support base.

The LDP's main opponents, the Democratic Party of Japan, are currently the largest grouping in the assembly with 54 seats, but are in disarray after their national drubbing last December.

Tokyo governor Naoki Inose, in whom the bulk of city power is vested, is not up for election, having won a four-year term in December.

Voting began at 7am (6am Singapore time) and the polls will close at 8pm.

Broadcasters are expected to provide exit polls indicating the likely result shortly thereafter.