The legislative building and a handful of office towers joined what organisers estimated would be around a million citizens who heeded a call to switch off their lights for three minutes at 8:00pm (1200 GMT).

But it was business as usual across much of the neon-lit city, with the downtown district, tourism strip and high-rise skyline remaining bathed in neon. Some bars and restaurants reverted to candles for several minutes.

While there appeared to be a delay in the onset of a nightly laser show across the city, government officials denied it was in support of the protest.

The government sparked outrage when it said it would not join the protest for fear of sending the wrong signals to the world's business and tourism communities.

"I'm generally disappointed that more lights didn't go out (downtown) but I'm proud that we at least got our message across," campaign coordinator Alastair Robins said after the brief protest.

The grassroots campaign, which Robins said was conceived while walking his dog one smoggy day, snowballed into a major event with retail giants promoting the blackout call in advertisements.

Local pop group At17 offered their help in galvanising support amomg youths.

The aim of organisers was to educate citizens on how their everyday activities, especially consumption of electricity, can have a direct effect on the environment.

"It is a very simple concept -- people can take their own action to help the environment," said Edwin Lau, director of Friends of the Earth Hong Kong, which provided support for the "Lights Out Hong Kong" campaign.

"We want people to think of where the energy they use comes from and get them thinking about alternative ways of producing energy that doesn't produce as much pollution," Lau said.

Smog reduced visibility in Hong Kong to less than one kilometer (about half a mile) on more than 50 days last year.

The government says the problem is mostly due to the industrialisation of southern China's nearby Pearl River Delta region. Green groups are pressing for tougher controls on Hong Kong's coal-burning power stations and diesel-powered buses.

Tour operators say visitors are increasingly complaining of pollution-related illnesses while business leaders say investors and executives are staying away because the smog is threatening their health and the economy.

Although Tuesday's event took place in clear evening skies, the day had begun in a blanket of grey smog.

In some parts of the city official pollution gauges reached "very high" levels Tuesday, prompting a government health warning that people with heart or repsiratory problems should stay at home.

All rights reserved. � 2005 Agence France-Presse. Sections of the information displayed on this page (dispatches, photographs, logos) are protected by intellectual property rights owned by Agence France-Presse. As a consequence, you may not copy, reproduce, modify, transmit, publish, display or in any way commercially exploit any of the content of this section without the prior written consent of Agence France-Presse.