Berlin's landmark Brandenburg Gate turned out its lights at 8:30 p.m. (1930 GMT) on Saturday, as more than 30 major cities in Germany took part in the symbolic Earth Hour 2010.
The one-hour switch-off, first held in Sydney in 2007, was organized by the World Wide Fund for Nature (WWF), expressing public concerns over climate change.
With people's countdown and applause, WWF Germany's executive boarding member Christine Kolmar and Berlin senator for environment Katrin Lompscher pulled down a symbolic giant switch together and the Brandenburg Gate went dark.
"As for confronting climate change, our precious time is running out," Lompscher told Xinhua.
"We hope this event can help Berliners realize their responsibilities over the planet's future, and try all means to safeguard our environment."
As lights went out, many people rode special-designed bicycle models before the Brandenburg Gate, lightening a panel with the image of "Berlin Bear" and the WWF's panda logo through electric wires between the two.
Kolmar believed the Earth Hour sends "a strong message" to people and world leaders. "Human joint actions are vital to protecting ourselves from global warming and horrible extreme weather," she said.
"I feel this activity is great," a nine-year-old German pupil Phil said. "We have to reduce emissions, and the Earth is fed up with greenhouse gases."
"The Earth Hour is successful in arousing people's attention on curbing emissions and living in an energy-saving style," environmental volunteer Julia told Xinhua, with twinkling candle in her hands. "But the key point is what to do after the dark hour. Can we change our habits and turn to be real green?"
Besides Berlin, Germany's Bonn, Munich and Cologne also participated in the switch-off. Well-known landmarks, such as the Cologne Cathedral, Heidelberg Castle and Dresden's Zwinger Palace, dimmed for the Earth Hour.
Organizers said a record number of 4,000 cities in more than 120 countries and regions voluntarily turn off their lights for one hour, like a relay race, from one time zone to another.