People who have seen the bus say it is painted gold. "It is now undergoing testing and commissioning," she said. "KMB will conduct road tests of the eBus to gauge its suitability for Hong Kong's operating conditions."

The specifications of the bus and the routes it is likely to run are unknown, though it is expected to be deployed in areas plagued by pollution such as Nathan Road in Kowloon.

KMB also plans to test the so-called gBus, which uses super-capacitator technology to charge up from overhanging power points at bus stops, on two routes in Kowloon. The bus was used during the 2010 World Expo in Shanghai. Unlike the battery-powered eBus, it can go only 10 kilometres without recharging.

Professor Eric Cheng Ka-wai, of the department of electrical engineering at Polytechnic University, said many challenges lay ahead for the eBus.

"Safety is the top priority, both in terms of the passengers and the vehicle itself," he said, citing public concern about a car crash involving a BYD electric taxi in Shenzhen that burst into flames.

Cheng said investment and careful planning would be needed to set up a charging network and fit the recharging to the bus operating schedules.

A rival electric bus provider, Great Dragon, says its first right-hand-drive bus will arrive in the city as early as next month and will be passed to a public utility for trials.

The Environment Bureau says a government-funded trial of electric buses starts next year.

In July, the legislature approved funding for procurement of 36 electric buses and related charging facilities for KMB, City Bus/New World First Bus, Long Win Bus and New Lantao Bus.

Previous attempts to introduce electric buses ended in failure more than a decade ago. In 2001, a few 14-seat electric minibuses were tested for six months. They proved hard to charge, sputtered going uphill and were expensive to maintain.