Lights at Sydney's iconic Opera House and Harbour Bridge were switched off on Saturday, along with lights in many high-rise office blocks and restaurants around Australia for Earth Hour 2008.
As many as 30 million people are tipped to switch off lights and televisions around the world to help fight climate change with around 370 towns and cities in more than 35 countries taking part in the event, organisers say.
Australians held candle-lit beach parties, played poker by candle light, floated candles down rivers and dined by candle light during Earth Hour.
One pub in southern Victoria state was offering free beer to anyone who came with a black balloon, to symbolise every individual's carbon footprint.
During the first Earth Hour in Sydney in 2007, more than two million businesses and households turned off their lights for one hour to raise awareness about climate change.
This year Earth Hour has gone global, with cities including Atlanta, San Francisco, Bangkok, Manila, Ottawa, Dublin, Vancouver, Montreal, Phoenix and Tel Aviv joining Sydney by switching off their lights.
Ionic buildings to be plunged into darkness include San Francisco's Golden Gate Bridge, Chicago's Sears Tower and Soldier Field Stadium football ground, as well as the 553-metre (1,815 ft) CN Tower in Toronto.
Earth Hour asks residents in participating cities to switch off lights and non-essential electrical items for one hour at 8 pm local time to rally public opinion about the carbon emissions from burning fossil fuels that scientists blame for causing global warming.
More than 3,500 businesses across the world have agreed to turn off their lights during Earth Hour 2008. McDonald's Australia has committed to turning off its Golden Arches nationally.
SEEING THE LIGHT
Suva in Fiji and Christchurch in New Zealand were the first two official participating cities to go dark in the Asia-Pacific.
In Christchurch, media reported about 2,000 people gathered in the city's Cathedral Square to show their support, with about 60 businesses taking part.
Energy distribution company Orion said power consumption in Christchurch dropped 12.8 per cent during Earth Hour.
Earth Hour was about more than one night, said Andy Ridley, executive director for Earth Hour.
He said it was about inspiring people to make daily changes that will help achieve Earth Hour's ultimate goal of reducing emissions by 5 per cent.
"What makes Earth Hour a unique event is that it brings together governments, business and householders who all play a part in switching off the lights," Ridley said in a statement.
During last year's Earth Hour in Sydney, essential lights were kept on for safety reasons, including street lights. Power provider Energy Australia said the event cut electricity consumption by 10.2 per cent.
Earth Hour organisers said they did not know how much energy would be saved globally from the 2008 lights off, but would calculate Australia's savings and announce it on Sunday.
In Bangkok, some of the city's business districts, shopping malls and billboards will go dark, although street lights would remain on. One major hotel is inviting guests to dine by candlelight and bookings were brisk, the hotel said.
Elsewhere in the region, NGOs said Japan was not on the Earth Hour list because they already had their own two-hour version of "lights-out" every June and December, during which the Tokyo Tower, some castles and other landmarks go dark. (Reuters)
Sydney switches off lights for Earth Hour