Big manufacturers' confidence is likely to have hit a 6½-year low in the September quarter, a Reuters poll has found, as the U.S.-China trade war and weakening global demand hit the business mood.

The Bank of Japan's quarterly tankan business sentiment survey is projected to show the headline index for big manufacturers' confidence fell to plus 2 in September from plus 7 three months earlier, the poll of 12 economists found.

It would be the third straight quarterly deterioration and the lowest value since March 2013, when the index showed minus 8.