The index, based on a survey of 19,500 Chinese firms, fell to 128.6 points in the third quarter, down 16.1 points from the same period last year. In the second quarter the index dropped 8.8 points from 137.4 points.
It was the first time China's business climate index fell below130 points since the outbreak of the Severe Acute Respiratory Syndrome (SARS) epidemic in early 2003. The 100-point mark is seen as a definition between depression and prosperity.
Compared to the same period last year, all sectors reported notable declines in business climate index, the NBS said.
If compared with the second quarter this year, all enterprises, except the service industry, reported declining business indices.
The information technology and software index, which remained at the top among all sectors, declined 15.3 points from the April-June period.
According to the NBS, the business index of China's listed companies plunged to 145.6 points in July-September, down 18.5 points from the second quarter.
In terms of company size, the index of large-sized enterprises fell the most. In the third quarter it was to 143.5 points, down 23.9 points year on year and 12.4 points from the second quarter.
The indices of medium- and small-sized enterprises were 118.5 points and 111.9 points, down 12.6 points and 8.9 points, respectively, from a year earlier.