Chinese authorities told the BBC that the journalist was detained to protect him from getting COVID.
"The epidemic has been effectively controlled," Shanghai's Vice Mayor Zong Ming said.
The latest steps have further frustrated residents, who were hoping a more than monthlong lockdown was finally easing.
The IMF reduced its forecast of Chinese growth this year to 4.4% from 4.8% due to the shutdowns, prompted by the ruling Communist Party’s "zero COVID" policy.
Access to Guangzhou, an industrial center of 19 million people near Hong Kong, was suspended this week.
The Chinese government is continuing to pursue its strict "zero COVID" policy to fight the current wave.
Officials in China's largest city announced an extended lockdown as COVID-19 cases continue rising.
The highly contagious omicron BA.2 form of the virus is testing China's ability to maintain its zero-COVID approach.
Shanghai’s Pudong financial district and nearby areas will be locked down from Monday to Friday as mass testing gets underway
It's the first of Disney's parks to reopen since the pandemic began.