A new study shows major Japanese manufacturers are more confident about business prospects than at any time since the March 11 earthquake and tsunami.

The survey, released every three months by the Bank of Japan, produced a confidence index of “plus two” among the large manufacturers, compared to “minus nine” in the previous survey. A positive number means more companies are hopeful than not hopeful.

The improved sentiment comes as Japanese companies have largely overcome supply-chain disruptions that forced many of them to cut back production after the earthquake. Production is now approaching pre-earthquake levels.

However, concerns remain about a strong yen, the eurozone debt crisis and economic weakness in the United States.

The bank also surveyed small and medium-sized manufacturers and large companies not in the manufacturing sector. All registered strong gains in business confidence, although only the non-manufacturers made it into positive territory.