Japan's core machinery orders plunged at the fastest pace of a seasonally adjusted 15.7 percent in December from the previous month, the government said Wednesday.The orders slid for the first time in three months to JPY 744.1 billion (USD 7.3 billion) following a 9.3 percent expansion in November, and marked the sharpest month-on-month decline since comparable data became available in April 2005, according to data released by the Cabinet Office.Core private-sector orders, which exclude volatile demand from electric utilities and for ships, are considered a key indicator of corporate capital spending in the next three to six months. By industry, orders by manufacturers dropped 17.3 percent percent month-on-month in December, and those from non-manufacturers also shrank 17.2 percent. Overseas demand, an indicator of future Japanese exports, gained 8.6 percent.The data came as concern grows that the planned sales tax hike April, from the current 5 percent to 8 percent, will cause negative impact to the world's third-biggest economy. Despite worsening data, the Cabinet Office maintained its basic assessment on the orders, saying, "Machinery orders are on a growth trend," it said, however they "significantly decreased in December." Looking ahead, the Cabinet Office projected that the orders will shrink 2.9 percent in the January-March quarter.