Many people were hospitalized as hundreds of people ran away from an unidentified gas that attacked a residential area in the southern province of Binh Duong on Thursday.
According to locals of in Quarter 1B of Thuan An Town, at around 6.30 p.m. they smelled gas which made their eyes teary.
Soon later they found that it was from the nearby Tico Joint-stock Company, which produces chemical substances and soap.
The gas leak intensified, so locals ran away from their houses. Many of them fainted and were rushed to hospital.
"It was a chaos. Many people fainted, and some people's faces got pale and vomited," 56-year-old Nguyen Dinh Tuyet, a local, said in the newswire VnExpress.
Tuyet said he also saw many people ran out of Tico.
According to the news source, all of the patients recovered and were released later the same day, except for two children who are still put under observation at Binh Duong General Hospital.
Initial information provided by the staff of Tico showed that the gas was sulfur trioxide which was leaked during an electrical problem, VnExpress reported.
However, Nguyen Thi Lieu, another local, was quoted as saying that a couple of months ago, they were also attacked by the same gas, but not as much as this time.
Thuan An Town's related agencies have launched investigations into the incident's cause.
Sulfur trioxide, in the gaseous form, is a significant pollutant and the primary agent in toxic acid rain. It causes serous burns on inhalation and ingestion since it is highly corrosive and hygroscopic.