BEIJING — China's courier sector posted robust growth momentum in May, according to an industry index.

The China express delivery development index came in at 344.2 last month, surging 73.5 percent from the same period last year, said the State Post Bureau in a report.

The country's courier sector saw faster expansion in May amid the large-scale resumption of business, with its business volume and revenue jumping over 30 percent year-on-year.

An estimated total of 7.3 billion parcels was delivered last month, up 39.6 percent year-on-year, the report showed.

The sub-index for service quality jumped 142.1 percent year-on-year to 622.4, while in key regions 76 percent of parcels took no more than 72 hours to reach their destinations.

The express delivery development trend sub-index saw a 38.2-percent year-on-year growth to 94, according to the report.

The expansion in the sector was partly due to a recent online shopping festival initiated by several government departments, the sales of which hit 182.51 billion yuan (about $25.72 billion).

Compiled on the basis of data from China's major logistics firms operating delivery services, the index reflects the overall business activities and trends in the country's courier sector.