In Paris, hundreds of monuments and buildings, from the Louvre and Notre Dame Cathedral to the Arc de Triomphe, all went dark. The lights on the Eiffel Tower were switched off for five minutes for safety reasons.

Combo photo taken on March 28, 2009 shows the Invalides when lights are turned off after 8:30 p.m. and turned on one hour later in the Earth Hour event sponsored by the World Wildlife Fund in Paris. Some 200 sites of historical fames and buildings, including the Paris City Hall, Notre Dame Cathedral, the Louvre, the Invalides, the Place du Pantheon, the Concorde Square, joined Saturday's Earth Hour event by dimming lights from 8:30 p.m. to 9:30 p.m. local time to highlight the global threat of climate change. [Zhang Yuwei/Xinhua]

Elsewhere across Europe, St Peter's Basilica in Rome and the Greek parliament in Athens all went dark.

In Brazil, Latin America's largest country, more than 60 cities including several in the Amazon region took part in the event.

In Rio de Janeiro, the iconic Christ the Redeemer statue was darkened, along with the beachfront of the Copacabana and a few other local sites.

In the Chilean capital of Santiago, lights went off at banks, the city's communications tower and several government buildings, including the Presidential Palace where President Michelle Bachelet hosted a dinner for U.S. Vice President Joe Biden.

In New York, lights in the landmark Empire State Building dimmed as clock struck 8:30 p.m. EST. As a symbolic action, the United Nations observed Earth Hour for the fist time at its headquarters and at other UN facilities around the world.

UN Secretary-General Ban Ki-moon, in a video-taped address to mark the event, called Earth Hour "a way for the citizens of the world to send a clear message. They want action on climate change."

"It promises to be the largest demonstration of public concern about climate change ever attempted," Ban said.

Earth Hour first started in Sydney in 2007, with just 2.2 million Sydneysiders taking part.

(Xinhua News Agency March 30, 2009)