More than 120,000 fake face masks exported from Shanghai - some of which were bound for African countries - were tracked down and destroyed by local customs officials as the public calls for a thorough investigation of the quality of masks sold in the domestic market.Photo: CFP

More than 120,000 fake face masks exported from Shanghai - some of which were bound for African countries - were tracked down and destroyed by local customs officials as the public calls for a thorough investigation of the quality of masks sold in the domestic market.

The confiscated masks were poorly made counterfeits of products designed by the Minnesota-based 3M Company, the China News Service reported on Monday.

3M said that the knock-offs were made from low-quality materials and may pose a threat to wearers' health.

In 2013, Shanghai police raided an additional eight criminal rings producing and selling counterfeit 3M-brand breathing masks.

Many Chinese condemned the counterfeit masks on social media, while some expressed concerns about the general quality of anti-pollution masks, which are in high demand throughout China against the backdrop of frequently occurring smog.

Chinese customers have snapped up anti-pollution products in recent years as the air pollution in China has worsened.

Consumers on China's biggest online shopping platform, Taobao.com, spent 870 million yuan ($135 million) on anti-smog products in 2013, according to the site.

"Public awareness of air pollution has been growing in the past few years. Chinese people are learning how to protect themselves from health problems caused by air pollution," said Dong Liansai, a Greenpeace air pollution observer.

According to Mu Ren, an agent for the Singaporean mask brand Totobobo in China, shoddy anti-air pollution products are not rare online. He also said that there are at least three kinds of counterfeit Totobobo masks.

"Face masks designed for air pollution require high-tech materials and specially designed filters, which can hardly be obtained by copycats. The fake masks can do little to keep out air pollutants," Mu told the Global Times on Wednesday.

"Phony masks that have not been inspected by health authorities can cause allergic reactions and may harm the wearers' health," Wang Jian, director of respiratory medicine at the Shanghai No.9 People's Hospital, told the Global Times earlier.

China's Standardization Administration released a draft of anti-pollution mask standards on June 24, stipulating acceptable materials, designs and filtration efficiency.

Many cities in northern China have been suffering under severe air pollution over the last few days. Beijing saw an average PM2.5 concentration exceeding 332 micrograms per cubic meter on Wednesday, reaching the heaviest pollution class in a six-tier pollution measuring scheme.