Hong Kong's first battery-powered public bus took to the streets Monday as part of a drive against the city's choking pollution.

Chief executive Leung Chun-ying has pledged to make pollution one of his top priorities during his five-year term, with an official report saying it was the "greatest daily health risk" to the city's residents.

But at least one local environmental group was sceptical about the government's anti-pollution committment, saying "one bus wouldn't make any difference" and that Hong Kong was lagging behind other global cities when it came to electric vehicles.

The new single decker bus revealed Monday was manufactured by Chinese automaker BYD and is powered by lithium iron phosphate batteries that take three hours to charge and give the vehicle a range of about 180 kilometres (110 miles).

The same company produced the southern Chinese city's first electric taxis, which were launched in May.

Secretary for the Environment Wong Kam-shing said the government was investing HK$180 million ($23 million) in the pilot scheme, helping to subsidise the purchase of 36 electric buses by the end of next year that will be run by private companies.

"The long term goal is towards zero emissions along the roadside," he told a press conference, without giving a timeframe for the possible expansion of the pilot scheme.

"We need to do it step by step," he said.

Kowloon Motor Bus, the largest operator involved in the trial scheme, said it would take time and money if it was going to transform its fleet of 3,800 buses, with each battery-run vehicle costing about HK$5 million ($644,700).

"Battery powered bus is still a new technology," KMB managing director Ho Tat-man said.

"We still need to collect a lot of operating data from the frontline for us to do detailed analysis, and to get customer feedback."

A study by the University of Hong Kong showed pollution-related illnesses killed more than 3,000 residents a year in the financial hub, with environmental groups blaming traffic emissions as the main source of the pollution.

New air quality objectives announced last year for seven pollutants including sulphur dioxide and carbon monoxide were criticised as too little, too late and in August last year the city choked under the worst smog on record.

Kwong Sum-yin, Chief Executive Officer of green group Clean Air Network, told AFP that Hong Kong was lagging behind other parts of the world in pushing for electric vehicles.

"One bus wouldn't make any difference," she said.

"We can look at other developed cities, such as Singapore and Tokyo -- there are way more electric vehicles. Even in China, Shenzhen has electric taxis."