Japan's core machinery orders unexpectedly fell for a second straight month in May, government data showed on Thursday, stoking worries about capital spending and the sustainable recovery needed for the Bank of Japan to raise interest rates.

The volatile leading indicator of capital spending fell 3.2% month-on-month in May, following a 2.9% drop in April and confounding analysts in a Reuters poll who expected a 0.8% increase.

The decline in machinery orders may be a bad omen for the BOJ's plans to normalize monetary policy as it embarks on unwinding its unconventional policy.

It raised rates in March for the first time since 2007 and decided in June to cut government debt purchases.

"Given fragile consumer spending and corporate investment, it will be difficult for the BOJ to raise interest rates at its upcoming policy review" scheduled for July 30 to 31, said Takeshi Minami, chief economist at Norinchukin Research Institute.

The central bank will wait until October to see if conditions are set for further rate hikes, Minami said.

"Japanese firms, particularly those in the service sector, may turn wary about boosting capital spending while increasing wages and labor-saving investment to cope with a labor crunch."

The Cabinet Office, which compiles the data, cut its view on machinery orders, saying there are signs a pick-up is stalling.

It marked the first downgrade in the assessment since the start of this year.

The core orders exclude shipbuilding and repairs, as well as electricity power generation, which tend to be more volatile.

Orders from overseas are also not counted as core orders, instead being categorized as external orders.

Core orders account for around one-third of the overall machinery orders, and external orders make up around 40%.

Orders from overseas jumped 9.1% month-on-month in May and 20.9% from the same month a year earlier.

By sector, manufacturers' orders rose 1.0%, and nonmanufacturers fell 7.5% partly because of the loss of demand in the communications industry for items such as computers, the Cabinet Office data showed.

Orders for chip-making machinery helped to drive up the numbers for manufacturers.

Compared with a year earlier, core orders, regarded as an indicator of capital spending for the coming six to nine months, increased 10.8% in May.

A Cabinet Office survey showed core orders grew 4.4% from January to March from the previous quarter but were expected to fall 1.6% in the second quarter.

Capital spending has generally been one of the few bright spots in Japan due to demand for labor-saving technology to cope with a labor crunch.

The government is aiming for domestic investment, including research and development, to top ¥100 trillion ($620 billion) by fiscal year 2027.

Gross domestic product data showed earlier this month that private nonresidential investment fell 0.4% in the January-March period, making capital spending and consumption the major culprits behind a sharper than expected economic contraction.