A private school in Shanghai has been told to stop using its food supplier after parents found expired goods and unhygienic conditions during a surprise inspection of its kitchen, police said on Saturday.

Parents raised concerns about Shanghai SMIC Private School on Wednesday after visiting their children at lunchtime and finding they had been given only two steamed buns and a small plate of cooked vegetables.

At a meeting with school leaders to discuss the issue two days later, some parents proposed a spot-check of the kitchens. They were shocked by what they found.

Pictures and videos shared widely online showed surfaces with rotten and moldy produce, including tomatoes and onions, and crockery and bottles piled up in baskets on the floor.

On closer inspection, parents also found that the expiration dates on the packaging for some products had been modified or covered up with new labels. The date on a bag of five-spice powder, for example, had been changed from November 2017 to May 2019.

The news triggered outrage among netizens, especially those with children, with some accusing the school of failing in its duty to protect the health of students and teachers.

Police officers visited the school in Pudong New Area over the weekend and confiscated food from the kitchen. Some 21 samples of raw ingredients and semifinished products have been sent for testing to the food standards authority.

The school was ordered to end its relationship with Shanghai Eurest Food Technologies Services, the food supplier, and submit a new lunch plan for students. It must also strengthen its internal management of food safety, police said.

Shanghai SMIC Private School, located in the Zhangjiang Hi-Tech Park, was founded in 2001 by Semiconductor Manufacturing International Corp, or SMIC. It serves more than 2,900 international students from 25 countries and regions from kindergarten to 12th grade. About 20 percent are the children of SMIC employees.

The school's website shows tuition fees range from 26,550 to 62,050 yuan ($3,830 to $8,940) per semester, not including lunch.

Eurest is a subsidiary of Compass Group UK, one of the largest catering providers in the world. It has supplied the private school for four years.

Authorities are now checking Eurest's business permits while inspections are being carried out at other schools it supplies, police said, adding that any illegal conduct will be subject to criminal punishment.

The Pudong government has said that all school canteens and kitchens will be strictly inspected.

"More parents are sending their children to international private schools in the hope they will grow up in a safe and inclusive learning environment," said the mother of a 7-year-old boy who asked to be identified only as Yuan.

"If their safety and health can't be guaranteed at school, how can we trust that such a place will help them develop the skills needed for future success?"