TOKYO (Reuters) - Japan's core machinery orders unexpectedly rose 2.9 per cent in September, government data showed on Thursday, and companies forecast only a modest decline in orders in October-December in a welcome sign that business investment will pick up.

The month-on-month rise in core orders, which exclude those of ships and electric power utilities, compared with a 1.9 per cent drop projected by economists in a Reuters poll. It followed a 4.7 per cent gain in August, the Cabinet Office data showed.

Companies surveyed by the Cabinet Office forecast that core orders will fall 0.3 per cent in October-December, after rising 5.6 percent in July-September, which was the second straight quarter of increases.

Compared with a year earlier, core orders, a highly volatile data series regarded as an indicator of capital spending in the coming six to nine months, increased 7.3 per cent in September, against a 1.3 per cent decline expected.

The Cabinet Office maintained its assessment of machinery orders, saying they are showing signs of moderate recovery.