The incident took place at 8:30am and nearly 60 workers fainted while hundreds more had to be immediately evacuated from the workplace, according to a preliminary report.
Some workers said they detected a strange gas-like smell and suffered a shortness of breath, nausea, vomiting and dizziness.
After being notified of the incident, local authorities and relevant agencies rushed to the scene to bring workers to hospital for emergency treatment.
Doctor Tran Viet Tiep, director of Vietnam-Sweden Hospital said the cause of the incident was still under investigation but gas poisoning is suspected as being a possible cause. He added that victims panicked and breathed rapidly but are now receiving treatment at the hospital.
Vu Xuan Dien, director of Quang Ninh Health Department said there were no signs of poisoning so far. Relevant agencies have examined the environment and requested that production be suspended pending further investigation.
As of 1pm, around 56 workers had been hospitalized at Vietnam-Sweden Hospital in Uong Bi city, Quang Ninh province.
Earlier on June 4, a gas poisoning incident occurred at another Yazaki plant in Dong Mai IP, where dozens of workers fainted and were sent to hospital for emergency treatment.