Students are paying attention in class. (Xinhua/Yao bin)

Over 200 students from Northeast China's Harbin city of Heilongjiang Province have returned home for observation after suffering vomiting and diarrhea suspected to have been caused by food hygiene problems. 

Harbin local media revealed that about 240 students from four primary and secondary schools in the city's Hulan district were sent to hospital after collectively experiencing vomiting and diarrhea on Wednesday morning.

By 2:45 am on Thursday, the last two students had left the hospital and returned home for rest and observation. By 7:00 am, the symptoms of the students who went to the hospital for examination had gradually eased and no serious harm was caused, the district officially reported. 

The students who did not go to the hospital were also in stable physical condition, the district added. 

After the incident, Hulan district immediately formed a special work team to carry out an emergency response. The local health authority quickly guided local hospitals to set up a treatment team with experienced medical staff, China Central Television (CCTV) reported.  

The local education bureau, health commission, market supervision bureau and public security bureau have gone to the four schools to carry out investigations, according to reports. 

Food samples from the four schools have been sent to Harbin's local center for disease control and prevention (CDC), and the cause of the incident is under investigation, CCTV said.

Global Times