Confidence at Japan's large manufacturers improved to its highest level in 13 years in the three months to June, underlining the most powerful economic recovery since the economic bubble burst in the early 1990s, according to the Bank of Japan's key business survey released Thursday.

The quarterly "tankan" showed the business confidence index for large manufacturers hit 22, up from 12 in the March survey and the fifth consecutive quarterly rise. The figure for June is the highest since August 1991, when the index stood at 25.

The business confidence index represents the percentage of companies reporting conditions are good minus those reporting otherwise.