The rapid rise of fast-fashion e-commerce retailers such as Shein and Temu is upending the global air cargo industry, as they increasingly vie for limited air-cargo space to woo consumers with rapid transit times, more than 10 industry sources said.

Shein, PDD Group's Temu and ByteDance's TikTok Shop, which recently began online shopping in the United States, ship the majority of their products directly from factories in China to shoppers by air in individually addressed packages.

And their growing popularity — Shein and Temu together send almost 600,000 packages to the U.S. every day, according to a June 2023 report by the U.S. Congress — is boosting air-freight costs from Asian hubs such as Guangzhou and Hong Kong, making off-peak seasons almost disappear and causing capacity shortages, the sources said.