From Sydney Harbour to the Empire State Building, cities and world landmarks plunged into darkness on Saturday as a symbolic energy-saving exercise unfolded across the globe.

The pyramids at Giza in Egypt, the Acropolis in Athens and the Houses of Parliament in London cut their electricity as part of "Earth Hour," a worldwide call for action to avert potentially devastating climate change.

Some 371 landmarks powered down worldwide, including the Malaysia's Twin Towers, Eiffel Tower, Niagara Falls, the Las Vegas casino strip and Beijing's "Bird's Nest" Olympic stadium.

The switch-off ended in Honolulu, capital of the US state of Hawaii.

Moonlit picnics & barbecues

The global event began dramatically as Sydney's iconic Opera House and Harbour Bridge plunged into darkness on Saturday night, killing their lights for an hour, followed later by the glittering Hong Kong waterfront.

Millions of people turned out in Sydney, while Melbourne, Australia's second-largest city, came to life with a pedal-powered concert and others enjoyed moonlit picnics and barbecues.

The global grassroots movement began in Sydney two years ago, when 2.2 million people switched off their lights.

Earth Hour has since grown to include 3,929 cities, villages and localities across the globe.

- AFP