BEIJING, Oct. 15 -- China's courier sector saw expansion in September, according to a monthly industry index.

The State Post Bureau said the monthly express delivery development index came in at 406.1 in September, up 15 percent year on year.

The sub-index for service quality grew 19.9 percent from a year earlier, the sub-index for development scale picked up 12.7 percent year on year, and the sub-index for development capacity went up 7.9 percent year on year.

With the arrival of China's annual online shopping festivals "Double 11" and "Double 12" later this year, the courier sector is expected to enter its peak season in the fourth quarter and maintain a rapid growth trend, said the State Post Bureau.

The index is compiled based on data from major logistics firms operating delivery services. It reflects the overall business activities and trends in the country's courier sector.