More than 100 people have sought medical treatment this week after suspected exposure to a pollutant in an area known as the "Chilean Chernobyl" for the environmental impact of heavy industry.
Local authorities declared an environmental emergency in the area, suspending classes and banning physical activity, after the Quintero Air Quality Station reported a concentration of sulfur dioxide (SO2) in the air five times the norm on Monday.
A total of 105 people -- among them 50 children -- have sought help in the towns of Quintero and Puchuncavi in the Valparaiso region, complaining of headaches, itchy eyes and throats, and nausea, the SMA environmental agency said late Wednesday.
The Quintero prosecutor's office has opened an investigation into the incident.
Quintero and Puchuncavi, two coastal towns with some 50,000 inhabitants combined, have been deemed "sacrifice zones" since 1958, when the Chilean government converted what was an fishing and farming community into an industrial hub.
Today it houses four coal-fired thermoelectric plants and oil and copper refineries.
Environmental group Greenpeace dubbed the area the "Chilean Chernobyl" after hundreds of people sought medical help for symptoms ranging from dizziness and headaches to vomiting blood and paralysis of the extremities in an episode in 2018.
On Wednesday, Chile's environmental superintendent Emanuel Ibarra ordered six companies operating in the area to "limit their productive activity, without harming the primary supply."
The companies include Chile's principal fuel company, Copec.
On Tuesday, the regulator also ordered measures to reduce pollution from the operations of state mining company Codelco -- the world's largest copper producer -- and the Aes Andina thermoelectric plant in the area.
Codelco, which is responsible for eight percent of the world's copper supply, said in a statement that its Ventanas smelter halted operations on Monday and will "maintain a voluntary suspension of operations" for maintenance.