As if to stress the point, grey smog blanketed the high-rise city as organisers made final appeals for citizens and corporations to switch off their lights for three minutes at 8:00pm (1200 GMT) to show their anger at worsening air quality.

"This is going to be the biggest protest in Hong Kong's history," said Lights Out Hong Kong campaign coordinator Alastair Robins.

"I hope it will force the government to actually do something about our terrible air pollution," British expatriate Robins added.

The grass-roots campaign, which Robins said was conceived over a drunken conversation in his local bar, has snowballed into a huge event, with the city's retail giants promoting the blackout call with free ads and publicity.

Political leader Donald Tsang's refusal to get involved -- despite recent calls for citizens to do their bit to clean the environment -- made headlines here Tuesday.

Tsang had been asked to suspend for the duration of the protest a nightly laser show for tourists that bathes the skyline in coloured light and fireworks.

He refused, saying that to do so would send the wrong signals "to the international community that protecting the environment is inconsistent with modern life".

Robins poured scorn on Tsang's remarks, saying he had missed a golden opportunity "unite the people and the government".

"I'm not angry, I am disappointed because this is something that the people are really concerned about," Robins said.

Local pop duo At17 were called on to galvanise young protesters.

"This is something that young people are passionate about because the pollution is really killing our city," said singer Ellen Loo.

The deteriorating air quality was obvious Tuesday as the skyline all but disappeared behind a grey haze of photolytic smog that in some parts of the territory sent the official pollution gauge into the "high" levels.

Pollution has become such a problem that smog reduced visibility to less than one kilometer (about half a mile) on more than 50 days last year.

The government claims the problem is mostly due to the industrialisation of southern China's neighbouring Pearl River Delta region. Green groups blame 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.

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