SHIJIAZHUANG -?A total of 135 students were hospitalized for stomachaches, diarrhea and fevers after drinking contaminated water at a middle school in North China's Hebei province, the local government said.

As of Tuesday, 50 students were still under medical observation, but all were in stable condition, the government of Longhua County said in a press release.

It said the other 85 patients had been discharged from the hospital after being treated on Monday.

The students, all from Zhangjiying Middle School, came down with high fevers, vomiting and diarrhea from Saturday to Monday.

The school has more than 800 students.

A preliminary investigation found the school's water source was contaminated by norovirus.

Noroviruses spread from person to person, through contaminated food or water, and by touching contaminated surfaces. It is one of the leading causes of foodborne-disease outbreaks in many countries.