CANBERRA - Billions of citizens from more than 130 countries are expected to turn off their lights on Saturday for the Earth Hour 2011, the event organizer told Australia's media on Thursday.

The Earth Hour event, organized by environment group World Wildlife Fund (WWF), was first started in Sydney of Australia in 2007 with 2.2 million Australians taking part to turn off their lights in aid of the environment.

By 2009, up to 1 billion citizens across the world had taken part.

According to Earth Hour spokesman Winston Su, this year, 133 countries had signed up for the event, with 13 of them taking part for the first time.

"We've built global awareness of the event," Su told Australia Associated Press on Thursday. "The aim was always to not use non- essential lighting."

All Australian cities are taking part in the 2011 event. The Opera House and Harbor Bridge in Sydney of Australia will power down for an hour.

Australian Prime Minister Julia Gillard recorded a message for Earth Hour, saying she was "going beyond the hour" by bringing in a carbon price.

"As well as switching off lights for Earth Hour, people who take part are pledging themselves to climate change action - big or small - for the next 12 months," Gillard said in the video message.

"My commitment for this year is simple: I will do everything in my power to deliver a carbon price. ... I believe 2011 is the year Australia will choose action. Everyone taking part in Earth Hour this year is helping to make sure this is so. Earth Hour is a wonderful example of Australian creativity and confidence at its best."

Further afield, international landmarks to be powering down include Times Square and the Empire State Building in New York, the Eiffel Tower in Paris, and the tallest building in the world, Dubai's Burg Khalifa.

In Asia, the authorities that have signed up include those of Bangkok of Thailand, Hong Kong of China, New Delhi and Mumbai of India.

In North America, New York, Chicago and Toronto would take part, along with most of South America's biggest cities.

Key European cities include London, Berlin, Paris, Rome and Moscow.