A customs officer uses a dog to check for illegal substances at an e-commerce industrial park in Hefei, Anhui province, that mainly deals with cross-border businesses.

A dog checks luggage at Haikou international airport in Hainan province.

Substances related to fentanyl, an opioid used to treat pain, have been rampantly abused in some countries, causing many deaths. (Photos: Xinhua, China Daily)