They also called on schools to refrain from increasing the burden on students, with measures to avoid long hours of studying online and learning beyond the curriculum.

Schools should not require students to register their attendance online or upload videos of their participation, the notice said, adding that students must be given a reasonable amount of rest time.

It emphasized that protecting students' eyesight must be a priority, with measures to expand rest periods and encourage physical activity.

Lyu Yugang, head of the Ministry of Education's Department of Basic Education, said schools must not use home-schooling to replace their normal curriculum.

"When the classes reopen, local authorities and schools must carefully assess the quality of the students' learning and come up with targeted teaching plans," he told a news briefing on Wednesday.

He also stressed the importance of extending more help to the children of medical workers fighting on the front line to curb the outbreak and rural children left behind by parents migrating to urban areas for jobs.

"We need to ensure that every student has already grasped the knowledge in online courses before starting new courses," Lyu said.

Despite the authorities' repeated reminders about the need to ensure adequate rest periods, Xin's parents are still worried about her eyesight.

To complete her online learning, Xin needs to use a laptop and a cellphone to receive messages from her teachers.

"We do not have other options. It was the only way to make sure she can keep up her schooling," said Zhou Ying, her mother.

"She also missed her classmates and kept asking when she could meet them. We could not give an answer."

Zhou said her daughter had already been using instant messaging tools to stay in touch with fellow students, which exacerbated their concerns about her eyesight.

"We can only hope that either I or her father can continue to be able to work from home. Otherwise we will have a babysitting problem," she said.

Chu Zhaohui, a researcher at the National Institute of Education Sciences, said it would be a better option for schools to use the time before schools reopen to encourage students to learn on their own initiative.

"The extended holiday has offered students an opportunity to make their own decisions, plans and arrangements," he said. "It will spur them to take more initiative, boost their confidence, exercise more self-control and improve their self-learning abilities."