To ensure their smooth operation, Shenzhen has built 510 bus charging stations and installed 5,000 charging facilities from 2009, according to the Shenzhen Transport Commission.

Besides "green" buses, Shenzhen is also promoting electric cabs with more than 12,500 running on its roads. The city is expected to replace its entire fleet of cabs with environmental-friendly ones by 2020.

"Electric buses and taxis play an important role in the city's fight against air pollution," said the commission's spokesperson. The commission said that the amount of carbon dioxide emitted by electric buses has decreased by 1.35 million tonnes annually compared with that discharged by traditional buses. Moreover, the electric transport system can alleviate the city's noise and heat effect, the commission said.

Currently, many Chinese cities are encouraging clean energy-powered transport as part of the country's efforts to protect the environment. Taiyuan, the city at the centre of the coal industry in north China's Shanxi Province, has made all its cabs electric, and the city plans to add 1,000 electric buses in 2018.