In Paris a minute's silence was observed for Japan as the city of light went dark, with illuminations switched off at the Eiffel Tower, Notre Dame cathedral, City Hall, opera houses and many bridges, fountains and public places.

Sydney's Opera House was the first of many global landmarks to go dark as the event got under way, as hundreds of millions of people prepared to follow suit to enhance awareness of energy use and climate change.

Others in their turn included Beijing's "Bird's Nest" stadium that hosted the 2008 Olympics, the London Eye ferris wheel, Times Square in New York and Brazil's Christ the Redeemer statue.

Many were switching off their floodlighting, advertising signs and other illuminations for an hour from 8:30 pm local time.

AFP