SOREL-TRACEY, Que. -- Five people that were taken to hospital Thursday morning after an explosion at the Rio Tinto iron and titanium plant in Sorel-Tracy, Que., have been now been released.

Company spokeswoman Claudine Gagnon says the workers were treated for shock at the hospital and discharged.

There was no immediate word on the cause of the explosion, which happened at about 4:30 a.m. ET at the metallurgical complex northeast of Montreal.

In total, about 1,400 people work at the complex. Gagnon said there were 192 people at work at the time of the incident.

She said the company will review what happened and what caused the explosion.

Rio Tinto is one of the world's leading metals and mining firms with about 50,000 workers in some 35 countries.

The Quebec operation manufactures raw materials for the titanium dioxide markets and produces high purity metal powders and pig iron.

Last year, the company announced it would spend $16 million to retrofit one of the furnaces at the metallurgical complex.