SHIJIAZHUANG - Some villagers were sickened Wednesday evening by gas leak after a chemical plant fire in North China's Hebei province, but exact number of casualties remains unknown, local officials said Thursday.

The accident occurred Wednesday evening when a benzenesulfonic hydroxide workshop of Hebei Jianxin Chemical Co Ltd caught fire at Lingang Economic and Technological Development Zone in Cangzhou city of the province, according to the management committee of the zone.

No deaths or injuries was reported at the site. But some residents at a downstream village named Xinzhuangzi developed such symptoms as chest tension and nauseating after they inhaled acid smog from the plant. Some villagers have been hospitalized for treatment and observation, but exact number of them is yet to be known.

Experts said that the fire, which was put out at around 9:00 pm Wednesday, was ignited by nitrobenzene created after sulfur trioxide leaked from the chemical workshop met humid air.

The chemical company was ordered by the management committee to suspend operation for overhaul.