By James Thornhill

SYDNEY, March 30 (Reuters) - More than half of Australian adults switched off their lights in major cities on Saturday as part of Earth Hour to raise awareness about climate change, organisers of the event said, citing a poll.

Cities across Australia took part in Earth Hour 2008, with iconic buildings including Sydney's Opera House and Harbour Bridge to Melbourne's Flinders Street station switching their lights off at 8 p.m. local time.

Around the globe, up to 30 million people were expected to have turned off their lights for 60 minutes by the time "Earth Hour" -- which started in Suva in Fiji and Christchurch in New Zealand -- completed its cycle westward.

More than 380 towns and cities and 3,500 businesses in 35 countries signed up for the campaign that is in its second year after it began in 2007 in Sydney, Australia's largest city.

In Canada, the 1,815-foot (553-metre) CN Tower in Toronto and the surrounding skyline were plunged into temporary darkness. In the United States, landmarks such as San Francisco's Golden Gate Bridge and Chicago's Sears Tower went dark in the closing hours of the event.

In the poll of more than 3,000 Australian householders, researchers found that 58 percent said they had at least switched their lights off for the hour, said global conservation group WWF, which coordinated the event.

Respondents to the poll by research consultants AMR International were less prepared to switch off the television, with only 30 percent doing so, although 46 percent said they had unplugged other household appliances.

"The overwhelming support for Earth Hour from Australians across the country has amazed us and shows the willingness of both business and individuals to start cutting emissions," said WWF-Australia Earth Hour Director, Andy Ridley.

"The polling only targeted people over 18 years of age and, given the popularity of Earth Hour among kids, the actual number of participants is likely to be much higher," he said in a statement.

In Bangkok, Earth Hour saved 73.3 megawatts of electricity, Deputy Bangkok Governor Banasopit Mekvichai told Reuters.

"Or simply put, about 2 million fluorescent lights were off," Banasopit said.

The lights were switched off on six main roads and three of the city's landmarks were also left in darkness, including the Temple of Dawn, the Rama VIII bridge and Ratchadamnoen Avenue.

In the southern New Zealand city Christchurch, energy distribution company Orion said power consumption dropped 12.8 percent during Earth Hour. (Additional reporting by Ploy Chitsomboon; Editing by David Fogarty)

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