Canada's largest cities went dark Saturday evening as the country celebrated international Earth Hour.

In Toronto, the CN Tower and the city's largest skyscrapers dimmed their lights at 8:30 p.m. ET, with hundreds of thousands of people across the city and its environs also taking part.

Earlier in the evening, Halifax Mayor Peter Kelly switched off the lights at city hall as Canada prepared to mark the 2009 edition of Earth Hour.

And in Edmonton, businesses and homeowners dimmed the lights as locals congregated in the city's central square to mark the event.

In total, about 250 cities and towns in Canada participated in the intentional blackout.

Designed to raise awareness about the threat of climate change, nearly 4,000 cities in 88 countries are expected participate in the event, which calls for all nonessential lights to be dimmed between 8:30 p.m. and 9:30 p.m. local time.

Interest in Earth Hour has risen dramatically since last year's event, in which 400 cities participated. Sydney threw a solo event in 2007.

From dimming the lights on towering Hong Kong skyscrapers to dialing down electric generators in Antarctica, millions of people around the world celebrated the event this year.

Organizers had feared that this year, Earth Hour would be overshadowed by the ongoing global financial crisis. However, the opposite appears to be true, according to Earth Hour executive director Andy Ridley.

"Earth Hour has always been a positive campaign; it's always around street parties, not street protests, it's the idea of hope not despair. And I think that's something that's been incredibly important this year because there is so much despair around," Ridley told The Associated Press.

"On the other side of it, there's savings in cutting your power usage and being more sustainable and more efficient."

The rise in Earth Hour's popularity comes as global leaders prepare to negotiate a new global warming treaty at the end of this year.

Negotiations are scheduled for December in Copenhagen, Denmark, to find a replacement for the Kyoto Protocol, which expires in 2012.

Revelers in Australia attended candlelit speed-dating events and watched outdoor concerts. Lights in Sydney Harbour dimmed, which left shadows dancing across the iconic Harbour Bridge and Opera House.

On the Chatham Islands, which are about 800 kilometres east of New Zealand, officials kicked off Earth Hour by turning off all diesel generators. The lights on Auckland's Sky Tower, the tallest man-made structure in New Zealand, shut off not long afterward.

About 44 cities and towns in New Zealand dimmed their lights, and more than 60,000 people attended an Earth Hour-themed hot air balloon festival in the city of Hamilton.

The country's 26-member winter staff team at Scott Base in Antarctica powered down to minimum safety lighting and switched off appliances and computers.

In China, residents participated in Earth Hour for the first time. Lights were turned off at Beijing's popular Olympic venues, such as the Bird's Nest Stadium and Water Cube.

Shanghai planned to cut lights in government buildings and along the city's waterfront. Hong Kong, Nanjing and Guangzhou were also participating.

However, the official Earth Hour website appeared blocked in Beijing, Shanghai and Tianjin on Saturday afternoon.

In Hong Kong, officials were to suspend the nightly "Symphony of Lights," which beams lights and lasers into the sky from 44 buildings along Victoria Harbour.

In Thailand, Prime Minister Abhisit Vejjajiva was to shut off lights along Khao San Road, a neighbourhood of bars and outdoor cafes in Bangkok.

As Earth Hour wound its way around the globe, the Great Pyramids in Giza were dimmed and partiers in Bonn, Germany, organized a candlelit cocktail party.

In Paris, the Eiffel Tower went dark, but only for five minutes because of security reasons as tourists were still on its visitor decks. France's largest city also dimmed the lights on 200 famous buildings, including the Notre Dame Cathedral and the Louvre.

In Germany, many cities were taking part in Earth Hour for the first time.

"Above all in the current economic crisis, we should send a signal for climate protection," said Berlin mayor Klaus Wowereit.

With files from The Associated Press