Japan's core machinery orders unexpectedly fell 19.5 percent in May from the previous month, government data showed on Thursday, casting doubt over the outlook for a pickup in capital spending.

The month-on-month decrease in core orders, a highly volatile data series regarded as an indicator of capital spending in the coming six to nine months, compared with economists' median estimate of a 0.7 percent gain in a Reuters poll of economists.

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That followed a 9.1 percent fall in April, data compiled by the Cabinet Office showed.

Compared with a year earlier, core orders, which exclude ships and electric power utilities, declined 14.3 percent in May, versus a 9.5 percent gain expected.

The Cabinet Office cut its assessment on machinery orders, saying the increasing trend was seen stalling.