People switched off lights across the world on Saturday, dimming buildings, hotels, restaurants and bars to show concern at global warming.
Up to 30 million people were expected to switch off their lights for 60 minutes by the time "Earth Hour" -- which started at 8 pm in Suva in Fiji and Christchurch in New Zealand -- completed its cycle westwards.
More than 380 towns and cities and 3,500 businesses in 35 countries signed up for the campaign that is only in its second year after it began in 2007 in Sydney alone.
"Earth Hour shows that everyday people are prepared to pull together to find a solution to climate change. It can be done," said James Leape of WWF International which was running the campaign.
"But we need to harness some of the cooperative spirit we've seen with Earth Hour to find a global solution."
Lights at Sydney's Opera House and Harbour Bridge were switched off and Australians held candle-lit beach parties, played poker by candle light, floated candles down rivers and dined by candle light.
In Bangkok some of the city's business districts, shopping malls and billboards went dark, although street lights stayed on. One major hotel invited guests to dine by candlelight and reported brisk business.
In Copenhagen the famed Tivoli Gardens said it would also switch off along with the City Hall.
In Britain some 26 town and city councils signed up to switch off non-essential lights as did several historic buildings including Prince Charles' private residence Highgrove House, London City Hall, Winchester Cathedral and even the Government Communication Headquarters radio monitoring station.
Google joins in
And in the age of the Internet, the UK arm of search engine Google too turned its home page black ahead of time with the message: "We've turned the lights out. Now it's your turn."
Floodlights were also to go out at landmarks in Budapest, including its castle, cathedral and parliament, and about 100 statues and museums.
The movement was then to jump the Atlantic to the United States and Canada where several cities including Chicago, San Francisco, Atlanta and Toronto signed up.
San Francisco's Golden Gate Bridge, Chicago's Sears Tower and Soldier Field Stadium football ground, as well as the 553-metre CN Tower in Toronto were due to be plunged into darkness. Even the lights at Niagara Falls were to go out.
Buildings account for about one-third of the carbon emissions that scientists say will boost global average temperatures by between 1.4 and 4.0 degrees Celsius this century bringing floods and famines and putting millions of lives at risk.
Organisers of Earth Hour said that while switching off a light for one hour would have little impact on carbon emissions, the fact that so many people were taking part showed how much interest and concern at the climate crisis had taken hold.
"This was only supposed to be in Australia again this year but we got bombarded with messages of interest to spread it far wider," said WWF's Jo Sargent. "Next year it will be even bigger."
(Additional reporting by James Thornhill in Sydney, Chisa Fujioka in Tokyo and Ploy Chitsomboon in Bangkok)