Four hundred liters of chlorine gas leaked from a chemical plant in Gumi, North Gyeongsang Province on Tuesday morning, leaving one person seriously injured.
Gumi is in a state of high anxiety since this is the third accident with toxic chemicals there in six months.
Although the environment authority said contamination levels were safe two-and-a-half hours after the leak, that was not enough to reassure locals, and hospitals were packed with anxious people.
Soonchunhyang University Gumi Hospital said 167 people had visited the emergency room by 5:30 p.m., most of them either working or living at or near the site.
They complained of sore throats, headaches and itchy skin.
Locals are still haunted by a hydrofluoric acid explosion at the Hube Global plant in September last year that killed five staff and saw 12,000 people report to hospital.
The Gumi municipal government claims it has completed a special inspection of 136 businesses dealing with toxic substance for over a month and found no problems.