Chinese customs seized over three tonnes of pangolin scales, state media said, in the country's biggest-ever smuggling case involving the animal parts.

Shanghai Customs found around 3.1 tonnes of pangolin scales mixed in with a container of wood products imported from Nigeria, state broadcaster CCTV reported Tuesday.

It estimated up to 7,500 of the creatures could have been killed.

The reclusive pangolin has become the most trafficked mammal on Earth due to soaring demand in Asia for their scales for traditional medicine and their flesh, considered a delicacy.

State media have previously said the scales fetch around 5,000 yuan ($700) per kilogram ($700) on the black market -- which would make the seizure worth more than $2 million.

Although the international pangolin trade is illegal in China and they are listed as one of the most-protected wild animals, law enforcement remains weak.

Pangolins are also farmed in the country and an online site selling traditional Chinese medicine offers them at 7,000 yuan per kilogram.

The scales are nothing more than keratin, the same substance that makes up fingernails. Yet it has been falsely touted as a cure for multiple ailments, including cancer, among some practitioners of traditional Chinese medicine.

Shanghai Customs arrested three suspects who were suspected of smuggling the scales from Africa since 2015, the report said.