LANZHOU, Oct. 24 -- Suspected food poisoning at a school canteen in northwest China made 49 students sick on Thursday, with 22 still under medical observation as of Friday afternoon, local authorities said.

Students suffered from vomiting, abdominal pain and diarrhea at around 7 p.m., one hour after dining at Xiaojin Middle School canteen in Qingyang City, Gansu Province. Of more than 700 student diners, 49 were affected, with 23 seriously, according to the local publicity office.

The local food and drug administration has taken samples of the ingredients, seasonings, dishes and leftover food from the canteen and sent them for examination.

As of 2:30 p.m. Friday, 27 students had returned to school. An investigation is under way.