Ninety-four students from grades 3 to 6 of a primary school in Shanwei, Guangdong province, were sent to hospitals for treatment after feeling gastrointestinal discomfort on Thursday, according to a statement released by the local education bureau.

As of Friday, 85 of those students have returned home. Nine students are still required by their parents to stay in the hospital for further medical observation, said the statement.

Hospitals opened green channels and promised to make every effort to help treat the children.

Local relevant departments, including education, health, market supervision, and public security, have established a joint task force to investigate the case and promised to open their findings to the public.

Zhang Zirou contributed to this story.