The government on Monday lowered its assessment of the country's economy for September to "weakening," the first downgrade in over two years, based on a key business index that worsened as a global chip crunch and supply chain disruptions hit automakers.

The Cabinet Office revised downward its view by one notch from "improving" in the previous month, the most optimistic expression in the five-level evaluation, as the coincident index of business conditions for the reporting month fell 3.8 points from August to 87.5 against the 2015 base of 100.

The index, which reflects the current state of the Japanese economy, fell for the third straight month, following 0.2 point and 3.1 point drops in July and August, respectively.