A man killed eight students and injured four others with a knife Thursday night in a high school in Ruzhou city of central China's Henan Province, report agencies.

"The students were all sleeping when the incident happened," an official was quoted as saying.

"Students and teachers are calm now, and classes are still being held as usual today," she told CNN.

Xinhua said the police are trying to nab the culprit, who escaped, and ascertain the motive behind the massacre.

China traditionally has enjoyed a relatively low crime rate, but has suffered a series of knife attacks in schools and day-care

centers in recent months, CNN said. The earlier assaults left one child dead and 42 people injured.

Earlier, Beijing had ordered all schools in the country to tighten security by hiring guards and upgrading surveillance devices, said one report.  

On Wednesday, a man who slashed 25 children with a kitchen knife at a school in eastern China was executed, CNN said. Though no one was killed in that attack, a court ruled that the penalty was justified because the violence was "especially cruel."