An explosion at a chemical plant in Gumi in the southern part of Korea killed at least four workers and injured eight others Thursday, police said.

The death toll may rise as some of the wounded are in critical condition, police said.

The blast broke out at around 3:45 p.m. at the Gumi National Industrial Complex in North Gyeongsang Province when the employees of Hube Global were unloading hydrochloric acid from a tank truck, according to the police. The Seoul-based company makes chemicals and materials for cosmetics and medicine.

An investigation is underway to determine the exact cause of the accident. 

"An unidentified explosion took place when the workers were trying to connect hoses to a 20-ton tank lorry with chemicals," a factory official told Yonhap News.

"It seems that the workers were killed because the tank lorry contained hydrochloric acid," a police official quoted as saying.

Hydrochloric acid is a transparent, highly corrosive liquid with a pungent smell and mainly used for rust removal and other industrial applications.  

Among the injured, six workers at a nearby plant and a resident in the neighborhood were hospitalized for inhaling toxic gases.

The police said they evacuated workers at other factories and 50 households around the area and distributed about 700 gas masks to prevent further casualties. Firemen have deployed motorized sprinklers to neutralize the poisonous emissions. The city government is carrying out cleanup operations to keep residue from running into the Nakdong River, one of the country’s four largest waterways.

The industrial complex also houses a number of companies producing televisions and other electronic components.

By Shin Hyon-hee (heeshin@heraldcorp.com)