Ten people were arrested after police raided a house in the poor neighbourhood where they believe the cocaine was sold.
At least 17 people have died in Argentina and another 56 were hospitalised after consuming cocaine that contained a poisonous substance, authorities in Buenos Aires province, where the incident took place, said.
Officials said on Wednesday they are working quickly to determine what the cocaine was mixed with, but warned those who have bought the drug over the last 24 hours to dispose of it.
Sergio Berni, the security chief for Buenos Aires province, told the television channel Telefe that authorities were trying to locate the toxic substance "to remove it from circulation."
Provincial security forces detained 10 people suspected of selling the drug after the first deaths occurred on Wednesday.
Packets of cocaine similar to those described by the victims' families were seized.
Turf war among rival groups
Early reports said victims suffered convulsions and sudden heart attacks.
Some local media outlets reported that the cocaine had been "cut" with a toxic substance, likely by a drug gang looking to cut costs and maximise profits amid a turf war with rival groups.
"We are waiting for the laboratory results and the results of the investigations of the people who have been detained," Berni said.
Health authorities said at least four of the victims were men aged between 32 and 45.
"There is a key ingredient that is attacking the central nervous system," Berni said.
His office said late in the day that emergency services were reporting new patients in "critical condition" being brought to the hospital.
Death toll feared to rise
The San Martin public prosecutor, Marcelo Lapargo, told Radio Mitre that 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."
Investigators fear the toll could rise, with some people who bought the cocaine unable to reach a care centre in time.
Lapargo said that this case was "absolutely exceptional."
He also said that the idea of a battle between drug traffickers was "conjecture" at this point.
Police clashed briefly with residents in a part of Tres de Febrero who were protesting the arrest of local young people in the drug raid.
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