ZHENGZHOU, June 15 (Xinhua) -- Forty-nine primary school students in Gushi county in central China's Henan Province fell ill and were admitted to hospitals this week, local government said Friday.

The students began to feel dizzy and nauseous on Tuesday. As of Friday, 17 have been receiving treatment in hospitals and 21 others are under observation. All of them are stable, according to the county government.

Investigation into the cause of the illness is underway.

The government has closed a plastic factory and taken raw material for testing as some parents suspected that the illness may be caused by pollutants discharged from the factory.