At least 15 people have been killed at the Love Parade electronic music festival in the German city of Duisburg, police have said.
Police said they had been trying to stop people reaching the parade area because of overcrowding.
But the revellers panicked at a tunnel entrance. A number of other people were injured.
Organisers of the Duisburg event had said they expected more than one million people to attend.
No evacuation
Duisburg police initially reported 10 deaths but have now raised the toll to 15.
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Reuters news agency quoted police commissioner Juergen Kieskemper as saying the situation had become "very chaotic".
He said police closed the parade area due to over-crowding. Those trying to get in were told via loudhailer to turn around, but panic broke out.
Emergency workers reportedly had difficulty reaching those crushed.
City officials were said to have chosen not to evacuate the grounds of the day-long festival immediately, fearing it might spark more panic.
Love Parade
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* Techno-parade celebrating club culture, held in Germany since 1989
* Originated in peace event in Berlin staged four months before fall of Berlin Wall
* Seen as an institution in Berlin through 1990s, but suffered from increasing tension with city officials
* Cancelled in 2004 and 2005
* Held in the Ruhr region of western Germany since 2007, with 2009 event cancelled
Many of those attending appeared unaware of what had happened.
The event attracts music fans from all over the world, with floats from Brazil, Russia, the Netherlands, Spain and Australia among other nations.
The floats had been expected to parade through the city for 10 hours.
Many top international DJs also perform.
The event began in Berlin in 1989 as a peace demonstration and developed into a huge open-air music festival.
Financial constraints and differences with Berlin officials led to the event moving to other German cities.
Sad news, RIP.