Jia Feng, former head of the Center for Environmental Education and Communication at the Ministry of Ecology and Environment, said the green design of mobile phones is also a concern.

Wearing trousers he bought in 1990 and holding a bottle he has used for two decades, Jia said it was a "great pity" for him to abandon a Nokia phone several years ago. A keen environmentalist, he has commuted by bicycle for years. He had no choice but to stop using the phone, because the app for shared bikes could not be installed on the device.

"Not all consumers need fast-speed mobile phones with a large storage capacity," Jia said.

If manufacturers can upgrade phone designs and enable new apps to be installed on old devices, this will greatly prolong the life of some handsets, he added.

It might not be difficult to put Jia's idea into practice, but it could be hard for environmentalists such as him to reverse the rapid rise in the number of phones no longer in use.

Cheng Huiqiang, an official at the National Development and Reform Commission's Department of Resource Conservation and Environmental Protection, said disused phones have become a type of electronic waste, and the stockpile is rapidly mounting in China and around the world.

"This type of electronic waste is the most difficult to dispose of," he added.

"Achieving highly efficient recycling, utilization and disposal of this large number of mobile devices is an urgent issue," Cheng added.

Shao, the Aihuishou employee, said customers sometimes bring more than 20 disused phones to his store after they find to their surprise that there is an outlet dedicated to receiving these devices, adding that they not only bring their own phones, but those of relatives.

"Some customers show a strong awareness of environmental protection. When they learn that our company can dispose of phones that are no longer needed, they say they will give all their idle devices to us for free," Shao said.