China's top 100 supermarket enterprises maintained growth in online sales last year, data from an industry association showed.

In 2021, online sales of the country's top-100 supermarkets amounted to nearly 100 billion yuan (about 15 billion U.S. dollars), up 40 percent year on year, according to the China Chain Store and Franchise Association.

The total number of stores owned by these enterprises gained 2.9 percent from a year ago to about 30,000, with 11 firms logging a year-on-year growth of over 5 percent in sales revenue and store numbers.

Due to adverse factors such as COVID-19, the top 100 supermarkets saw declines in customer flow and per-customer transactions last year, said the association.

Their sales narrowed 2.6 percent year on year to 907.6 billion yuan in 2021, showed the data.