TOKYO (AFP) - Japan said on Friday it is moving to speed up the impact of a US$50 billion (S$63.29 billion) stimulus package aimed at countering any slowdown from a looming sales tax hike.

The rare move - which sets out a timeline for spending a big chunk of the special budget - comes days before the release of fourth-quarter growth figures.

They will mark the first annual data since Shinzo Abe swept to power on a ticket to restore Japan's fading status as a global economic superpower.

The prime minister's high-profile policy blitz, dubbed Abenomics, helped sharply weaken the yen and stoked a huge stock market rally last year as the once-anaemic economy outpaced G7 nations in the first half of 2013.

But the sales tax rise - seen as key to chopping Japan's eye-watering national debt - has sparked fears it would derail a recovery in the world's third-largest economy.

On Friday, Finance Minister Taro Aso said Tokyo has set a spending timeline for public works projects to safeguard against the increase to an 8.0 per cent tax in April, from 5.0 per cent now.

The targets would affect roughly 3.4 trillion yen (S$42billion) of the spending, which includes construction projects and corporate subsidies.

"We have requested that roughly 70 per cent of it be spent by the end of June and to finish 90 per cent of it by the end of September," Aso told reporters in Tokyo.

"By asking ministries to strongly encourage speedy implementation of the extra budget, we hope to be fully prepared for the downside risk related to the consumption tax hike," he added.

The spending will be spread across various levels of government.

Japan's latest growth figures will come as the Bank of Japan kicks off a two-day policy meeting on Monday, with policymakers expected to hold fire on their monetary easing plan.

But there is growing speculation the central bank will have to expand its already unprecedented injections of vast sums into the financial system to head off the impact of the new sales tax.