SANTIAGO, Sept. 10 (Xinhua) -- Chile's government on Monday took over the monitoring of air quality in two towns in the central province of Valparaiso, after hundreds were taken ill by a toxic cloud.

Environment Minister Carolina Schmidt presided over the handover of nine air-quality monitoring stations in Quintero and Puchuncavi.

The move was "the first concrete step of a comprehensive plan to decontaminate" the air affecting communities, Schmidt told reporters.

Hundreds of people have fallen sick in recent weeks due to unidentified toxic gases leaking from a local industrial park. The government was forced to issue a yellow alert for the zone, suspending classes and setting up emergency healthcare centers.

Local residents reported dizzy spells, vomiting and intense headaches.

Refineries and industrial plants belonging to the national oil company ENAP and the National Copper Corporation (Codelco) have been momentarily idled while investigators try to determine the source of the toxic fumes.

The comprehensive plan to clean up the air in the two towns was announced by President Sebastian Pinera last week, and is expected to be implemented in the next 90 days.???