A 21-year-old man died after an accident at a huge alcohol-drenched party organised on Facebook -- one of two such events held simultaneously in two French cities that drew nearly 20,000 people.
The gatherings, which the organisers call "giant cocktail parties," took place in Nantes and Montpellier and a part of a dangerous new trend.
The man fell about 20ft (6m) to his death apparently while trying to slide down a railing of a staircase on a bridge, according to the prosecutor's office in the western city of Nantes.
Police said the man, who has not been identified, died at the Nantes hospital hours after his fall in the early hours yesterday.
The party, that began on Wednesday night in Nantes' city centre, was held at the same time as a giant party in Montpellier, in southern France, which drew an estimated 10,000 revellers.
Nantes' regional prefect Jean Daubigny said 57 people were hospitalised after drinking too much. Police said 41 people were jailed.
"Regrettably, we saw some people who had totally lost control of themselves," Daubigny said. Among those treated by rescue workers were children aged 14 and 15, he said.
Because such events are organised anonymously on the social network site Facebook, authorities cannot work with organisers to ensure safety, he said.
In fact, the Nantes prefecture got wind of the gathering and forbid the sale and transport of alcohol in the city centre on Wednesday night. In France, large public gatherings need prior authorisation to take place.
Scenes of the party in Montpellier were shown on YouTube.
But Paris police are already braced for a giant cocktail party planned for May 23.
Police headquarters posted its own Facebook note, warning that the event to be held at the Champ de Mars, a grassy esplanade near the Eiffel Tower is illegal -- as is drinking alcohol there.
It noted that 14 people were hospitalised after a similar event recently in the Breton city of Rennes.
Police have warned that those organising such large gatherings without a permit risk a six-month prison sentence and a €7,500 fine.