Japan's key gauge of the economy stayed above the boom-or-bust line of 50 percent for the fifth month in a row in June, thanks to continued robustness in output-related indicators, the government said Monday in a preliminary report.

According to the Cabinet Office, the coincident index stood at 77.8 percent in the reporting month, compared with 100 percent in May. A reading above 50 percent is considered a sign of economic expansion, while a reading below that signals contraction.

"The coincident index is improving and it is possible the economic phase has changed," said Yoshihiko Senoo, director at the Cabinet Office's Economic and Social Research Institute, maintaining the government's official view from May. "However, it should be noted that the brisk production-related indicators owe largely to foreign demand, so moves in overseas economies and domestic demand will have to be closely monitored from now."