(CNN) -- Authorities in Ecuador have banned alcohol sales in an emergency measure to stop contaminated drinks from reaching consumers after at least 21 people died.
Officials announced the 72-hour national dry law Sunday after detecting alcohol poisoning cases in several parts of the country.
Hospitals treated more than 100 people who fell ill after drinking bootleg liquor over the past week, the country's government said, and at least 21 people died as a result of apparent poisoning.
Investigators determined that the liquor contained methanol -- an industrial-grade alcohol not intended for human consumption, Ecuador's Public Health Ministry said.
"It is a potent poison that can in small quantities, including a quarter of a cup, cause the death of the individual that consumes it," Health Minister David Chiriboga told reporters.
The liquor was sold in unlabeled bottles, with no indication of its contents or where it originated, Los Rios Gov. Jesus Narvaez told CNN affiliate Ecuavisa.
Doctors in the province first began seeing cases of alcohol poisoning last Tuesday, Ecuador's government said. By Sunday, 103 patients showing symptoms had showed up at local hospitals.
Authorities in Los Rios implemented a curfew, shut down bars and confiscated hundreds of unlabeled bottles containing bootleg alcohol, Ecuavisa reported.
The liquor "was massively consumed" during a festival in the town of Urdaneta, Los Rios, Ecuador's government said in a statement.
The 21 patients who died all haled from Los Rios, but similar poisoning cases have also been reported in at least four other areas, the government said.
Authorities have arrested the liquor seller and continue investigating, police said.