The second night of a major electronic music festival being held in Buenos Aires was cancelled following the deaths of at least five people of suspected drug overdoses, while another five were critically ill.
Health officials said that two people in their 20s died during the Time Warp festival on Friday and three others died in an ambulance or at hospital. Most of the critically ill youths were reportedly in comas.
"They are all in very grave condition, intubated," Dr Alberto Crescenti, director of the Emergency Medical Attention System in Buenos Aires, told the Todo Noticias station. "They are not breathing on their own."
He said doctors are trying to discover what caused the deaths.
A festival-goer told Todo Noticias that he saw a young man convulsing for 15 minutes and calling for security.
On Saturday, officials in Buenos Aires announced they had closed the Costa Salguero Centre where the second night of the two-night festival was to be held.
Time Warp organisers confirmed that Saturday night's show had been cancelled.
"We express our deepest condolences to the families and friends of the people who passed away. The cause of this tragedy will take some time to determine. The show is cancelled for tonight," said a statement released on the festival's website.
Time Warp, which began in Germany in 1994, was being held in Buenos Aires for the third year.
Police in the province of La Plata told The Associated Press that officers had intercepted a bus carrying party-goers to the festival and confiscated a large quantify of designer drugs, including 182 ecstasy pills, doses of LSD, marijuana, poppers and cocaine. Two people were arrested.