Police had failed to stop the underground event, set up in two warehouses in Lieuron, south of Rennes in Brittany on Thursday, which drew around 2,500 people.
But the prosecutors office said police had detained two people, both born in 1998, neither of whom had any previous convictions, as part of efforts to identify the organisers.
They were also carrying out a search at one address and had so far turned up a sum of money that appeared on first analysis to be part of the proceeds from the event, and drugs, said prosecutor Philippe Astruc.
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Police had seized the material and had also booked more than 1,200 for a variety of offences, he added.
Such mass gatherings are strictly prohibited across France to prevent the spread of Covid-19, and a nationwide 8:00 pm curfew — which was not lifted for New Year — applies across the country.
Techno music had blared out during the night from the warehouses, which had been transformed into illegal nightclubs for partygoers who had flocked to the site from across France and even abroad.
The local prefecture said on Saturday the music had been switched off and sound systems dismantled after two nights and the first revellers began leaving the site before dawn.
By 10:15 am it was under the control of police, the local prefecture said. Interior Minister Gerald Darmanin said in a tweet that police had seized a truck, sound equipment and generators from the site of the “illegal rave party”.
The large police presence at the site had led to the break-up of the event “without violence”, he added.
French Gendarmes evacuate the last partygoers who attended the rave. JEAN-FRANCOIS MONIER / AFP
The regional prefect, Emmanuel Berthier, said 800 people had been booked specifically for coronavirus-related offences such as failing to respect the curfew restrictions or wear masks, or for participating in an illegal assembly.
Police had fined several hundred others for use of narcotics, he told reporters.
'We had to party'
Police on access roads were checking all those leaving the site, on foot or in vehicles, using torches to check their eyes for signs of drugs use, an AFP photographer said.
French Gendarmes pat down a reveller after breaking up the rave in Lieuron about 40km (around 24 miles) south of Rennes, on January 2, 2021. JEAN-FRANCOIS MONIER / AFP
Police reinforcements continued to arrive and close off the site in a calm atmosphere on Saturday morning, the photographer said.
“It's been a year since we could do anything,” said 24-year-old partygoer Antoine. The salesman was part of a group of five from Brittany that attended the rave.
With drawn faces but with beers still in their hands, the group said they “had come to celebrate the 31st here because it was a huge party”.
“We knew what we were risking… we had to party, for a year everything has been stuck,” said one of the group, a 20-year-old waitress.
Alexis, a 22-year-old baker, said “at one point you say to yourself 'I am going to force my New Year'.”
He added that the rave had even been reported in the New York Times, saying “it was the biggest party of the year”.
'Lives in danger'
French authorities have been worried about mass rave parties throughout the pandemic, but New Year's Eve was a particular concern.
On Thursday night the police had tried to “prevent the event but faced fierce hostility from many partygoers” who set one of their cars on fire and threw bottles and stones, the prefecture said Friday.
First aid workers had distributed hand gel and masks at the event to try and limit the spread of the coronavirus.
A man undergoes a rapid antigen test for the Covid-19 after the evacuation by French Gendarmes of the last partygoers who attended the rave in Lieuron about 40km (around 24 miles) south of Rennes, on January 2, 2021. JEAN-FRANCOIS MONIER / AFP
The regional health authority in Brittany noted the “high risk of the spread of Covid-19” at the event, and called on those who took part to undergo coronavirus tests and self-isolate immediately for seven days.
The prefecture said in a tweet that a testing centre had been set up in a gymnasium in Lieuron.
“They have put their lives in danger, their health, they must now protect those around them,” it said.
The French government, facing the threat of a new wave of Covid-19 infections, announced on Friday it was extending its overnight curfew by two hours in 15 regions to help combat the virus, starting it at 6:00 pm instead of 8:00pm.
The country recorded around 20,000 new cases and 133 deaths on Friday, bringing the total number of fatalities to almost 64,800.