Shanghai authorities battling an outbreak of COVID-19 have erected mesh barriers outside some residential buildings, sparking fresh public outcry over a lockdown that has forced much of the city's 25 million people to stay home.

Images of white hazmat suit-clad workers sealing entrances of housing blocks and even closing off entire streets with roughly 2m-tall green fencing went viral on social media on Saturday, prompting questions and complaints from residents.

"This is so disrespectful of the rights of the people inside, using metal barriers to enclose them like domestic animals," said one user on social media platform Weibo.

One video showed residents shouting at workers setting up fencing from their balconies, who later relented and took them away. Other videos showed people trying to pull the fences down.

"Isn't this a fire hazard?" said another Weibo user.

Most of the barriers appeared to have been erected around compounds designated as "sealed areas", which are buildings where at least one person has tested positive for COVID-19 and so whose residents are forbidden from leaving their front doors.

It was not immediately clear what prompted authorities to resort to barriers, but a notice dated Saturday from one local authority shared online said it was imposing "hard quarantine" on some areas.

Reuters was not able to verify the authenticity of the photos, videos or notice.

The Shanghai government did not respond to a request for comment.