Three workers were killed and 12 others injured Friday when a water tank burst during a stress test at a polysilicon plant construction site inside Samsung Fine Chemicals, police said.

Hospital officials said the death toll could rise as some of the injured were in critical condition.

According to the police, the 1,300-ton water tank was being filled for the third day to detect any cracks or defects in it. The steel tank exploded when about 1,000 tons of water were injected.

Investigators suspected the tank was unable to bear the load. Samsung Engineering was building the tank for SMP, a joint venture between Samsung Fine Chemical and MEMC of the United States.

The workers were hit by flying debris from the tank and its supporting structures, the police said.

Samsung officials were criticized for holding back the scale of the accident, initially announcing that five to six workers sustained injuries. They later changed the number of victims after the police announced details.  Reporters were also blocked from approaching the scene.

(Yonhap News)