SYDNEY, March 31 (Reuters) - Sydney landmarks turned off their lights for an hour on Saturday, throwing icons such as the Sydney Opera House into darkness as part of a campaign to cut greenhouse gas emissions.

Restaurants set candle-lit dinners, the city's tallest building offered special tours on an open-air skywalk and the Sydney Youth Orchestra began its first concert of the year in darkness.

Around the city, hundreds of businesses and more than 50,000 homes signed up for the night, while parties and star-gazing events were planned along the harbour.

"We think that signal, the darkness of Sydney, will flash not only around Australia but right around the world, and send a very positive signal that we can do something," Greg Bourne of environment group and organiser WWF Australia said ahead of the event.

The one-hour power-down was designed to raise awareness of carbon emissions to combat global warming, and is part of a campaign to have Sydney cut its greenhouse gas emissions by 5 percent over the next year.

Bourne said he hoped the event would spread to other parts of Australia and could eventually be taken up globally.

Not everything in the city came to a halt, though. Essential lights were kept on for safety reasons, while a view over the Sydney skyline showed it was dimmed but not darkened. Street lights remained on.

And for people who didn't want to turn off all their power, local television offered "live coverage" of the event.

WWF said it would work out after the event how much power was saved.

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