China's courier sector registered expansion in May, according to a monthly industry index.

The State Post Bureau said the monthly express delivery development index came in at 370.9 in May, up 37.8 percent year on year.

The sub-index for service quality grew 78.5 percent from a year earlier, the sub-index for development scale picked up 17.8 percent year on year, and the sub-index for development capacity went up 8.3 percent year on year.

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.