Eighteen-year-old Ren Jinhao raced across a basketball court before making a shot cheered by his teammates.

In their sweat-soaked school uniforms, Ren and his classmates at a boarding school in Shijiazhuang, Hebei province, have kept their campus alive while the city of 11 million has been in pandemic prevention lockdown.

"We now have PE lessons on Tuesday, Thursday and Saturday," said Ren, who will take the national college entrance exam this summer.

"It helps protect our eyesight and allows us to breathe fresh air after staring at the smart blackboard for hours."

As part of a citywide lockdown to curb a recent surge in COVID-19 cases, the Shijiazhuang Foreign Language School has been sealed off from visitors since Jan 6.

About 600 of its 2,000 students and staff members, including 477 boarding students, were stranded inside, school authorities said.

Those on campus have been tested twice for COVID-19 since it was sealed off as part of a citywide testing campaign to detect coronavirus carriers.

All results came back negative, the school said.

The citywide stay-at-home order, which has been extended three times over the past two weeks, has amplified the homesickness of students stranded on campus.

To ease students' anxieties, school administrators have temporarily increased the number of PE classes as part of a broader curriculum reform amid the lockdown.

"City authorities first said the lockdown would be three days. It was then extended by a week and more recently prolonged again," said principal Pei Hongxia, who started teaching at the school when it was founded in 1994.

"We've never sealed off the school in its history before the coronavirus," she said, adding that the school had told psychological counselors to return to campus ahead of the lockdown.

To ensure a virus-free campus, Pei said, it has implemented preventive measures including frequent body temperature checks and the enforcement of rules on wearing masks, washing hands and maintaining social distance.

Ren said he and some of his classmates were worried about their parents after being kept on campus.

"The residential community where my parents live has been labeled as a medium-risk region," he said.

To ease such concerns, Ren said, head teachers had helped students get in touch with their parents through phone or video calls, given that students at the school are not allowed to have mobile phones on campus.

In addition to more PE classes, school authorities added more reading classes and appreciation sessions for music and documentaries to keep students engaged.

They have also arranged class meetings to help students stay informed about developments outside.

Alessandro Rojas Rivera, a Costa Rican teaching Spanish at the school, said he has encouraged his boarding students to learn a musical instrument or do something new as a diversion from the pandemic.

Having been in China for more than nine years and witnessed epidemic control measures in many other countries, Rivera said he was confident about China's containment measures, which have successfully stamped out many earlier outbreaks.

He has also sought to educate his students about the relationship between personal freedom and society's collective well-being.

"People in China will quickly follow government directives because they can always see there's a reason behind them," Rivera said.