A man fell to his death after taking part in a mass cocktail party which was organized over the Internet and drew almost 10,000 revelers, the prefecture for Nantes in western France said on Thursday.

The death is the first on record as a result of Facebook aperitifs -- giant outdoor drinking parties whose popularity has exploded in the last six months and which are organized over the online social network.

This must be stopped. It's quite dark, it's not a party, people came to get smashed, among them 15-year-old adolescents, Nantes deputy mayor Jean-Marc Ayrault told RTL radio.

Maybe it is based on good feelings at the outset but you can see that something is happening which is no longer controllable and could end in tragedy, he said, calling the death profoundly sad.

The 21-year-old man, who was drunk, landed on his head after falling over the railing of a staircase leading down from a bridge, after apparently trying to slide down the banister.

Such parties take place across France and often turn into mass drinking binges, sparking concern with authorities who are struggling to curb the phenomenon. Also on Wednesday, another party in the southern city of Montpellier drew around 11,000.

Another giant drinks party is planned for May 23 at the Champs de Mars in Paris, according to the event's Facebook page.

MASS BENDERS

Ayrault demanded the party's organizers be found and called on the interior ministry to set up a roundtable with mayors, health services and students to tackle the phenomenon.

Local authorities in Nantes, who were not consulted by the party organizers, had issued an order restraining the transportation and sale of alcohol on Wednesday night. Enforcement of the order proved impossible given the scale of the crowd, police said.

The inquiry, which will be carried out under the justice authorities, will let us know exactly the cause of death, the Loire-Atlantique region prefecture said in a statement.

Firemen and first aid workers picked up 93 partygoers at the Nantes party, 57 of which were hospitalized. Forty-two people in total were detained for peddling narcotics, theft and violence. One policeman was lightly injured, the prefecture said.

We will do everything to identify the organizers, Nantes national prefect Jean Daubigny told a news conference. (Writing by Sophie Taylor; Editing by Jon Hemming)