They joined Copenhagen and Aarhus, Manila, Fiji's capital Suva, Chicago, Tel Aviv, Christchurch, Toronto, Odense and Aalborg, as well as major Australian cities including Melbourne, Perth, Brisbane and the national capital Canberra.

"If we see the same participation levels around the globe that we did in Sydney, then we can anticipate more than 30 million people involved," said Andy Ridley, Earth Hour's executive director.

Earth Hour asks residents in participating cities to switch off lights and non-essential electrical items for one hour at 8 p.m. to raise awareness of carbon emissions that scientists blame for causing global warming.

During last year's Sydney event, restaurants used candles and lights were turned off in homes and major landmarks, including the Opera House and the Harbour Bridge.

This year, Ridley said, other iconic buildings to be plunged into darkness would include San Francisco's Golden Gate Bridge, Chicago's Sears Tower and Soldier Field Stadium football ground, as well as the 553-metre (1,815 ft) CN Tower in Toronto.

"Climate change is a truly global issue and people around the world are demanding action," he said.

During last year's Earth Hour in Sydney, essential lights were kept on for safety reasons, including streetlights. Power provider Energy Australia said the event cut electricity consumption by 10.2 percent.

(Editing by David Fogarty)