Sydney's iconic Opera House and Harbour Bridge went dark Saturday at the start of Earth Hour, followed by cities across Asia in a global switch-off aimed at revitalising efforts against climate change.
Harbour ferry horns blared to signal the energy-saving event, which is supported by 4,000 cities in a record 125 countries and includes 1,200 famous landmarks from the Forbidden City to the pyramids to the Las Vegas Strip.
"From Brazil to America, to Canada, all the way down to Australia, Japan and India -- it's a really diverse set of countries taking part this year," Earth Hour executive director Andy Ridley said.
Sydney's office buildings plunged into gloom at 8:30 pm (0930 GMT), setting off a rolling wave of darkness which will sweep the globe in a boost for the environmental movement after December's disappointing Copenhagen UN talks.
The WWF-run event had officially begun nearly three hours earlier when New Zealand's Chatham Islands switched off their diesel generators, leaving just 12 street lamps burning. It will eventually end in Samoa after nearly 24 hours.
On the way, most of the world's top landmarks, from the Eiffel Tower to the Empire State Building and the Leaning Tower of Pisa, will turn off the lights to show their support for energy conservation.
Beijing's Forbidden City and Bird's Nest Stadium were among the participants along with dozens of cities in China, the world's biggest carbon polluter, where giant panda Mei Lan is an Earth Hour ambassador.
Hong Kong's renowned neon waterfront dimmed as did office buildings in Jakarta, Seoul and Tokyo.
In Japan, the city of Hiroshima turned off the lights at 30 sites, including the Hiroshima Peace Memorial.
Also known as the Atomic Bomb Dome, the former exhibition hall was one of the few buildings to survive an atom bomb attack during World War II.
More than 100 students lit candles and arranged them to spell out "Peace and Eco", on the ground near the dome, clapping when the backdrop plunged into darkness, a city official said.
About 300 participants gathered in central Jakarta to light hundreds of candles and lanterns set out in the shape of the number 60 -- representing the 60 minutes of Earth Hour. About 100 buildings in the Indonesian capital had pledged to turn off their lights.
Indian cities Delhi and Mumbai were also due to join the switch-off.
Historical monuments across the country were turning off floodlights while a rock concert was organised to take place at New Delhi's landmark monument India Gate.
Bollywood celebrities joined the call for action on the environment.
"As responsible citizens of this planet, it's extremely crucial for us to address the colossal problem of climate change through ensuring responsible action," said Bollywood star Abhishek Bachchan.
India is expected to be one of the hardest hit by rising temperatures and changes in rainfall patterns that experts warn could affect its food security and displace many communities.
London's Big Ben and Manchester United's Old Trafford football ground are set to take part amongst Europe's best known spots including Paris's Notre Dame cathedral and the Trevi Fountain in Rome.
In America, some 30 states are on board with Mount Rushmore, San Francisco's Golden Gate Bridge and Chicago's 110-storey Sears Tower all due to go dark.
But in Bangkok, city authorities were ordered to halt their Earth Hour campaign for security reasons, as anti-government protesters held another major rally.
Earth Hour started in 2007 in Sydney and now enjoys widespread support both from the public and big business, including Google, Coca-Cola and McDonald's.
This year, even users of ubiquitous Twitter and Facebook can show their support with special applications that turn their displays dark.
In December, two weeks of UN talks in Copenhagen failed to produce a binding commitment to limit global warming or set out concrete plans for doing so, in a setback for the environmental movement.

Copyright 2010 AFP Global Edition