A closely watched index of confidence at major Japanese companies slumped more than expected in March, sending stocks down in trading in Tokyo on Friday.

The "tankan" index for large manufacturers fell to 6 in March, down from 12 in December, according to the Bank of Japan's quarterly survey. Analysts polled last week by Japan's Kyodo News service predicted it would fall to 8.

Japan's big exporters have been hit by a double whammy of a slowing Chinese economy and a rising yen.

The index measures the percentage of responding companies that say business conditions are better minus the percentage that say they are worse. So an index level of 6 means slightly more companies are optimistic than pessimistic. Companies can also respond that conditions are unchanged.

The index for large non-manufacturing companies, such as construction, retail and services, fell to 22, down from 25 in December.

The survey covered 10,930 large, medium and small companies, of which 1,087 were large manufacturers and 1,043 were large nonmanufacturers.