One minute brightly lit, the next plunged into darkness -- iconic landmarks around the world will cut their lights Saturday for the "Earth Hour" campaign against climate change.
Organisers expect hundreds of millions of people across the globe to turn off their lights for 60 minutes on Saturday night -- at 8:30pm local time -- in a symbolic show of support for the planet.
Many of the world's most iconic attractions, including Sydney Opera House, the Empire State Building and the Eiffel Tower will take part.
"What started as an event in Sydney in 2007 with two million people has now become a tradition across the country and across the world," Dermot O'Gorman, head of WWF-Australia, said.
"It's now an organic, people-powered movement... which is fantastic."
Last year more than 150 countries participated in the event which saw some of the world's most iconic landmarks dim, and this year the movement has spread to Palestine, Tunisia, Suriname and Rwanda.
Newcomers to be plunged into darkness include Copenhagen's Little Mermaid, the statue of David in Florence and Cape Town's Table Mountain.
In Australia, where Earth Hour originated with an appeal to people and businesses to turn off their lights for an hour to raise awareness about carbon pollution, the Sydney Opera House and Sydney Harbour Bridge will be among the first sites to participate globally.
This year Earth Hour Australia is asking participants to "switch off for good" and move to renewable energy. As part of the push Sydney Opera House won't go dark at 8:30 pm (0930 GMT) but will instead glow a deep green.
With restaurant diners eating by candlelight, Outback communities going dark and iconic buildings standing in shadows, O'Gorman believes Earth Hour has played a part in drawing attention to energy use.
"We've always heard anecdotally that it has made people change their actions and look at their impact on the planet in a more considered way," he said.
"Earth Hour has always been about empowering people to realise that everybody has the power to change the world in which they live, and thousands of people switching to renewable energy is a perfect example."
Sydney's lights out will be followed by countries across the globe, with the Petronas Towers in Malaysia, the Bird's Nest in Beijing, and the Burj Khalifa all participating.
In China, Shanghai's famous Bund will turn off its lights while in the central city of Wuhan, the Yangtze River bridge will be plunged into darkness.
In Japan, daily illuminations of the city's signature Tokyo Tower will be switched off, with visitors able to pedal bicycles to generate power to illuminate an egg-shaped art work.
In Japan's northeast local residents are set to light candles to both show support for the campaign and mourn victims of the 2011 quake-tsunami disaster, organisers said.
In Singapore, the affluent city-state's skyline will darken for one hour from 8:30pm (1230 GMT) as more than 100 buildings take part, while Hong Kong's famous skyline will also dim..
Earth Hour will also see famous landmarks such as the Eiffel Tower, the Brandenburg Gate, London's Buckingham Palace, the Empire State Building in New York and Niagara Falls take part.