"It was the first time I had tried a livestreaming app, and I felt quite nervous," the 50-year-old, who has taught math for 28 years, told the streaming app Pear Video.

Footage of a biology teacher in Jilin province using a glass door and a swab as teaching aids in his online class has also gone viral.

While some teachers are struggling with new education methods, students and parents have complained about the amount of time being spent onscreen and of low learning efficiency.

Sun Hui, a translator in Beijing whose daughter attends secondary school, said, "From morning to evening, she cannot leave her desk and keeps staring at the screen."

To reduce screen time, Sun bought an online printer to provide her daughter with study materials. Statistics from e-commerce platform Suning show that sales of printers have surged in recent weeks.

Amid criticism that online education has significantly increased the workload for students and teachers, the Ministry of Education said schools should not add an "unnecessary academic burden" to primary and secondary students through online classes.

Such courses should include infection prevention knowledge, psychological health and educational activities, rather than just subjects that place students under extra pressure, the ministry said.

No online classes should be provided to children at kindergartens, and parents of primary school students in lower-level grades can decide whether their children take such classes. For students in higher-level grades, schools should limit the amount of time spent on e-learning and the quantity of material, according to the ministry. It emphasized that protecting students' eyesight must be a priority through the introduction of measures to extend rest periods and encourage physical activity.

It also said schools should make good use of existing online teaching materials, rather than giving teachers an additional workload.

The education authority in Guangdong has issued a guideline for online classes, stating that such lessons should be limited to 20 minutes, with rest breaks and eye exercises included.

Lyu Yugang, head of the Ministry of Education's Department of Basic Education, said, "Online courses are only temporary measures taken during the epidemic, so when the new semester begins, schools should not replace classroom teaching with such classes."