Northland Secondary School in Yishun is investigating why a group of students were down with stomach infection on Thursday.

School principal Tan Siew Woon told The Straits Times yesterday that 14 students said they had vomited and suffered stomach pains.

A Secondary 1 student, whose classmates were taken to hospital, said the class had just finished recess at 11.20am on Thursday when some students started feeling sick during a science lesson.

"People were suddenly going to the toilet and some started puking," he said.

The affected students were taken to hospital by ambulance and accompanied by staff members. Most of the students were diagnosed with a stomach infection, said Madam Tan.

A Singapore Civil Defence Force spokesman said the students were taken to KK Women's and Children's Hospital and National University Hospital around noon.

According to the principal, eight students were discharged in the evening, and six were admitted for observation. Most of the affected students were from lower secondary classes.

All the students are recovering well and there have been no new cases reported in the school.

"As a precautionary measure, the school has closed the canteen for inspection and thorough cleaning... The affected classrooms and toilets have also been cleaned and disinfected," said Madam Tan.

The school canteen will reopen on Monday.