A doctor attends patients at one of the hospitals in the outskirts of Buenos Aires, Argentina, on Wednesday. AP

Apparently adulterated cocaine killed 20 people and seriously sickened 74 others in Buenos Aires suburb, health officials said early on Thursday

Officials said they were working quickly to determine what the cocaine was mixed with, but warned those who bought the drug over the last 24 hours to dispose of it.

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Experts were still analysing the drug to determine what was in it that caused the deaths. Judicial officials said one hypothesis being considered was that the cocaine was intentionally adulterated as part of a settling of scores between traffickers.

Police officers examine packages allegedly containing drugs seized during a raid in Taller Puerta 8 shantytown. AFP

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."

"There is a key ingredient that is attacking the central nervous system," Berni said.

About 10 people were arrested after police raided a house in the poor Tres de Febrero neighborhood where they believe the cocaine was sold.

Police said that the cocaine was sold in the poor neighborhood "Puerta 8” in San Martín — a suburb to the north of Argentina’s capital — and that a dozen people had been arrested.

Security forces stand guard during a raid in Taller Puerta 8 shantytown on Wednesday. AFP

"This event is absolutely exceptional. We have no precedent,” San Martin Attorney General Marcelo Lapargo told cable channel Todo Noticias. "If the situation has escalated and the nature of trafficking has changed to the point where this becomes commonplace, I hope I never see it again.”

Packets of cocaine similar to those described by the victims' families were seized. The drugs were taken to a laboratory in La Plata, the capital of Buenos Aires province, for analysis.

Authorities issued an urgent warning early Wednesday after three separate hospitals reported several deaths and serious cases of poisoning.

Several of those being treated told doctors they had taken cocaine together.