CANBERRA, March 31 (Xinhua) -- Iconic sites including Harbor Bridge and Opera House in Sydney, Australia's largest city, were plunged into darkness for an hour Saturday night as part of the city's actions to fight global warming.

    Except essential lights for public safety, other lights of many buildings, shops and houses throughout the city were switched off in a symbolic gesture to highlight the problems of global warming.

    The "Earth Hour," organized by World Wildlife Fund (WWF), an international environmental conservation organization, has launched a 12-month campaign aimed to reduce Sydney's greenhouse emission by 5 percent.

    Over 2,000 companies and 70,000 individuals and households signed up to the event on the website of "Earth Hour."

    Australian Broadcasting Corporation radio quoted Greg Bourne from WWF as saying the organization is hoping the "Earth Hour" campaign will become a worldwide event.

    "Everyone really now knows in Australia that climate change is the most important challenge facing us environmentally, socially and indeed economically, and (they) just want to get on and do things," he said.

    "So to my mind this is the opportunity for people to say 'lets all do stuff together'," he added.