Another 56 people have been hospitalized, a government source told Reuters, adding that more are seeking hospital care in eight of the province's municipalities due to the toxic cocaine.

The source said the death toll - currently from the towns of Hurlingham, San Martin and Tres de Febrero - will likely rise further.

Buenos Aires province, the country's most populous, is home to many suburbs of the national capital of the same name.

Officials believe some of the victims suffered from opioid intoxication, according to a statement from the province's health ministry released on Wednesday.

The number of those hospitalized with serious illness is "constantly rising," it added.

Provincial security forces detained some people suspected of selling the drug after the first deaths occurred on Wednesday.

Some local media outlets reported that the cocaine had been "cut" with a toxic substance, likely by a drug gang looking to reduce costs amid a turf war with rival groups.

"We are waiting for the laboratory results and the results of the investigations into the people who have been detained," SergioBerni, the province's security minister, told local television.

Reuters could not immediately reach the police and courts for further information.

The local government of Tres de Febrero said in a statement it was aware of people falling seriously ill due to "allegedly adulterated cocaine" and was working with emergency services and hospitals to prevent more deaths.

It urged people to discard any drugs bought recently, especially those with symptoms of confusion, convulsions or loss of consciousness.

"This isn't a normal investigation," San Martin prosecutor Marcelo Lapargo told local news outlet La Naction+, citing expedited police raids aimed at removing all the tainted cocaine.

"What mattered most today was to stop the sales to prevent further deaths."