Lights went out at Sydney's famous Opera House and Harbour Bridge on Saturday for Earth Hour 2009, a global event in which landmarks and homes go dark for an hour to highlight the threat from climate change.
Australia first held Earth Hour in 2007 and it went global in 2008, attracting the involvement of 50 million people, organisers say. Environmental group WWF, which started the event, is hoping one billion people will take part this year.
"The primary reason we do it is because we want people to think, even if it is for an hour, what they can do to lower their carbon footprint, and ideally take that beyond the hour," Earth Hour executive director Andy Ridley told reporters at Sydney's Bondi Beach.
Among the more than 80 countries taking part this year are newcomers like industrial powerhouse China and Asian industrial hub Singapore.
Organisers said several new countries signed up in the hours before the event, which aims to encourage people to cut their energy use and curb greenhouse gas emissions from burning fossil fuels.
In the Vatican, the dome of St Peter's Basilica will go dark, as will Egypt's Great Pyramids, the Eiffel Tower in Paris and New York's Empire State Building. Other global landmarks that will switch off the lights include the Petronas Towers in Kuala Lumpur, the London Eye and the Bird's Nest Stadium in Beijing.
Organisers said the remote Chatham Islands was the first place where supporters turned the lights off for an hour at 8.30 pm, followed by New Zealand and Fiji.
Lights at Sydney's Opera House and Harbour Bridge were switched off at 8.30 pm(0930 GMT) to the sound of horns on the harbour, with supporters holding candlelit dinners to watch the event.
"We are sitting here near the harbour. There are about 60 or 70 people here having a picnic got the candles out," an Earth Hour spokesman told Reuters.
In Melbourne, supporters organised a bicycle powered concert.
Organisers are calling Earth Hour a 'global election', with switching off the lights a vote for the Earth and failure to do so a vote for global warming.
In the Thai capital, Prime Minister Abhisit Vejjajiva will push a button to switch off the lights at Khao San Road, Bangkok's bustling, "backpackers' ghetto". Lights will also go out at Bangkok landmarks such as the Grand Palace and Temple of the Dawn from 1300 GMT to 1400 GMT.
The Bangkok Metropolitan Administration expects electricity usage in the city of 8 million people to drop by 30 per cent during that hour, or 1,384 megawatts.
Luxury hotels and restaurants plan to serve candle lit dinners with guests being asked to turn off room lights.
In Singapore, one hotel chain is encouraging guests to sleep naked, or without air conditioning. Some hotels are also offering candle lit dinners, while bars have cut the price of drinks during the event.
Lights will also be dimmed at landmarks in India, including the Reserve Bank in Mumbai and scores of other buildings in the city.
In Kuala Lumpur, a Malaysian mall is marking the global Earth Hour climate change initiative by dimming its lights and offering tickets to one of the world's most polluting sports to well heeled shoppers.
WWF says it will present the results at a conference on climate change in Copenhagen later this year, where governments will try to seal a successor agreement to the Kyoto Protocol on climate change.