The Hong Kong legislature building before (top) and during (bottom) the shut down

But environmentalists behind the campaign said they were disappointed at the scale of the three-minute black-out they had called for.

Some restaurants and bars resorted to candle-light, but office towers, tourist venues and sports stadiums remained bathed in neon.

"It wasn't what we were hoping for," said organiser Alastair Robins.

The "Lights Out" campaign had called on businesses, organisations and individuals to plunge the city into darkness at eight o'clock in the evening (1200 GMT) on the eighth day of the eight month - drawing on the positive symbolism of the number eight in Chinese.

The aim was to raise citizens' awareness of how their every day activities - particularly their use of energy - affect the environment.

Smog problem

Although the legislative building heeded the call, the protest failed to garner the mass support needed to create the visual spectacle the organisers had been seeking.

Smog levels in Hong Kong have reached record highs in recent years

"There was a bit of a dim," said Mr Robins, who watched the scene from Victoria Peak - Hong Kong island's highest point, "it wasn't great".

But he said the event had succeeded in getting the protesters' message across.

Hong Kong leader Donald Tsang had refused to back the black-out, saying it would damage Hong Kong's image as an international tourism and business centre.

Seventy percent of the air pollution comes from factories across the border in South China, many of them owned by Hong Kong people.

Air quality in Hong Kong has deteriorated in recent years, with visibility reduced to less than 1km (about half a mile) on more than 50 days last year.

Vehicle emissions trapped in the canyons made by tall buildings make up the rest.