Fifteen school students in Hangzhou, East China's Zhejiang province, have tested positive for COVID-19, said the city's health authorities on Monday.

The cases — 10 at a primary school in Xihu district and five at a secondary school in Gongshu district — were all infected for the first time, according to the authorities.

The two schools announced that in-person attendance for infected students and those in close contact with them has been temporarily put on hold as per COVID-19 prevention and control plans formulated after China optimized COVID-19 response measures in December last year.

They are isolated cases, said an official with Hangzhou's COVID-19 prevention and control command center, and does not signify the start of a new wave of infections.

Meanwhile, 12 students at a primary school in the city's Shangcheng district reported symptoms of fever and were found to be a cluster infection of influenza. In-person attendance and teaching schedules for these students and their classes have been rearranged as per health protocols.

Parents are advised to take their children to get antigen tests in time should they have any fever and similar symptoms, said the command center.

But as it is currently also a period of high incidence for H1N1 and norovirus infections, children who develop these symptoms do not necessarily mean they have contracted COVID-19, it added.

The center has urged residents to continue observing good hygiene habits, including washing hands frequently, wearing masks properly and maintaining proper ventilation.