The sequence of concerts in nine cities aimed at raising awareness of climate change, dubbed Live Earth, has reached Europe, with gigs in Hamburg and London kicking off on Saturday afternoon.
Sydney and Tokyo were the first two cities to host concerts, organised by former US vice-president Al Gore, whose documentary on global warming, An Inconvenient Truth, won an Oscar earlier this year.
The global event, which will go on for 24 hours, is expected to reach more than two billion people via television, radio and the Internet, and starts a three-year campaign to "heal the planet", in Gore's words.
Gigs in Johannesburg and Shanghai preceded the two European concerts, with events in Washington, New York and Rio de Janeiro wrapping up the marathon.
Among the artists who agreed to perform are the Red Hot Chili Peppers, Metallica, Smashing Pumpkins, Dave Matthews Band, Beastie Boys, Foo Fighters and Chris Cornell.