Landmarks around the world plunged into darkness in a global push to act on climate change.
Lights were turned off at 8.30pm local time to mark Earth Hour, organised by the WWF. To start the annual event, diesel generators were switched off on the Chatham Islands, a small archipelago off the east coast of New Zealand.
Lights then went out at Sydney's Opera House and Harbour Bridge. Asia followed with lights at landmarks in China, Singapore, Thailand and the Philippines dimming as people celebrated with candle-lit picnics and concerts.
Other iconic landmarks falling into darkness this year include the Eiffel Tower, Christ the Redeemer statue in Rio de Janeiro, Table Mountain in Cape Town, CN Tower in Toronto and the MGM Grand Casino in Las Vegas.
Among the landmarks taking part in Britain are Nelson's Column, the Forth Bridge, the Millennium Stadium in Cardiff, and the London Eye. The public is also being urged to get involved in their own homes.
"We are sitting here near the harbour. There are about 60 or 70 people here having a picnic," an Earth Hour spokesman said in Sydney. The organisers suggested people in Britain took part with picnics, acoustic gigs and pub quizzes in the dark.
Earth Hour began in Sydney in 2007, when more than two million homes and businesses switched off their lights for an hour. A year later, 50 million people switched off their lights, with the Golden Gate Bridge in San Francisco, Rome's Colosseum and the huge billboard in Times Square, New York, all standing in darkness.
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