HONG KONG—Chinese authorities have detained a FedEx Corp. pilot in the southern city of Guangzhou, elevating pressure on the express shipping giant that is already in Beijing’s crosshairs amid a U.S.-China trade war.

The pilot, a former U.S. Air Force colonel named Todd A. Hohn, was detained a week ago while waiting for a commercial flight to his home in Hong Kong after flying deliveries throughout Asia from the FedEx regional hub in Guangzhou, people familiar with the matter said.

A...