TOKYO (Reuters) - Japanese big manufacturers' business sentiment likely stayed steady in the three months to September, while non-manufacturers' confidence weakened slightly, a Reuters poll showed on Friday, reflecting concerns over the global economic slowdown.

The Bank of Japan's (BOJ) quarterly tankan business sentiment survey is expected to show the headline index for big manufacturers' confidence stood at plus 13 in September, unchanged from the June survey, the poll of 16 economists found.

"China's economic slowdown and the impact from typhoons weighed on business sentiment of big-manufacturers," while a recovery in auto production supported morale, economists at Daiwa Institute of Research noted.

The sentiment index for big non-manufacturers likely edged down but stayed solid at plus 32 in September from plus 33 marked in June survey.

While strong demand and wage recovery underpinned service-sector sentiment, labour shortages and natural disasters hurt their mood, analysts said.

Big companies will likely raise their capital spending plans by 11.9% for this fiscal year to March 2025, up from 11.1% projected in the June survey.

Confidence among both big manufacturers and non-manufacturers over the outlook was likely to ease slightly, the poll showed.

The BOJ will publish its tankan survey at 8:50 a.m. on Oct. 1 (2350 GMT on Sept.30).

Markets are closely watching the timing and pace of future rate hikes by the BOJ after the central bank on Friday kept short-term interest rates steady.

A separate data will likely show the Tokyo-area core Consumer Prices Index (CPI) data, which excludes volatile fresh food, rose 2.0% year-on-year in September, slowing down from 2.4% in August, the poll showed.

The government will announce the consumer inflation data for Tokyo area on Sept. 27.

(Reporting by Kaori Kaneko; Editing by Kim Coghill)