At least 20 people have died and 74 were hospitalised in serious condition after ingesting cocaine that had apparently been mixed with a toxic substance, in what authorities have called a possible poisoning.
Authorities were scrambling to determine what substance the cocaine had been cut with and on Wednesday were warning anyone who bought the drug within the last 24 hours to throw it away.
Possession and personal consumption of cocaine have been decriminalised in the country, while transporting and selling it are still illegal.
On Wednesday, Sergio Berni, the security chief for Buenos Aires province, told the television channel Telefe that authorities were trying to find the tainted cocaine “to remove it from circulation”.
Samples of the cocaine had been sent to a laboratory in La Plata for analysis.
“There is a key ingredient that is attacking the central nervous system,” Berni said.
Late on Wednesday, crowds waited outside hospitals in Buenos Aires for updates on their loved ones. Three separate hospitals reported several deaths and serious cases of poisoning.
Beatriz Mercado told the AFP news agency she had found her 31-year-old son, one of the victims, lying face-down on the kitchen floor.
“He was almost not breathing, his eyes were rolling back,” she said. She took him to the hospital, where he was on life support as of Wednesday evening.
“I hope in God, nothing else, a miracle.”
Authorities said at least 18 of those hospitalised required intubation.
Meanwhile, police arrested at least 12 people in the Tres de Febrero Partido section of San Martin, a low-income suburb north of the capital.
Residents of the neighbourhood began burning tyres to block roads, protesting what they called the random detention of innocent people.
Judicial officials have said one hypothesis is that the drug was poisoned in a conflict between traffickers, according to The Associated Press.
However, the San Martin public prosecutor, Marcelo Lapargo, told Radio Mitre the theory was “conjecture” at this point.
Amid concerns the death toll could rise, he said authorities’ main concern “is to be able to communicate, so that those who are in possession of this poison know that they should not consume it”.