At least 20 people have died and 74 have been hospitalized in serious condition after ingesting cocaine apparently mixed with a toxic substance, in what authorities said was a possible poisoning.
Authorities were working to determine what substance the cocaine was cut with and on Wednesday warned anyone who purchased the drug in the past 24 hours to throw it away.
The possession and personal use of cocaine has been decriminalized in the country, while its transport and sale are still illegal.
On Wednesday, Sergio Berni, the head of security for the province of Buenos Aires, told Telefe television that authorities were trying to find the contaminated cocaine “to remove it from circulation”.
Cocaine samples had been sent to a laboratory in La Plata for analysis.
“There’s a key ingredient that attacks the central nervous system,” Berni said.
Late Wednesday, crowds waited outside hospitals in Buenos Aires for updates on loved ones. Three separate hospitals reported several deaths and serious cases of poisoning.
Beatriz Mercado told AFP news agency she found her 31-year-old son, one of the victims, lying face down on the kitchen floor.
“He was hardly breathing, his eyes were rolling back,” she said. She took him to the hospital, where he had been on life support since Wednesday evening.
“I hope in God, nothing else, a miracle.”
Authorities said at least 18 of those hospitalized required intubation.
Meanwhile, police arrested at least 12 people in the Tres de Febrero Partido neighborhood of San Martin, a low-income suburb north of the capital.
Neighborhood residents began burning tires to block the roads, protesting what they called the random detention of innocent people.
Law enforcement officials have said one hypothesis is that the drugs were poisoned during a dispute between traffickers, according to The Associated Press.
However, San Martin prosecutor Marcelo Lapargo told Radio Miter the theory was “guesswork” at this stage.
While the death toll could rise, he said authorities’ main concern “is to be able to communicate, so that those in possession of this poison know not to consume it”.