(Adds details on Beijing measures in second paragraph)

By Brenda Goh and Jacqueline Wong

SHANGHAI, April 24 (Reuters) - Shanghai authorities battling an outbreak of COVID-19 have erected fences outside residential buildings, sparking fresh public outcry over a lockdown that has forced much of the city's 25 million people indoors.

The largest district in Beijing, meanwhile, will require everyone living or working in the area to take three COVID tests this week, and put more than a dozen buildings under lockdown, after the Chinese capital reported 22 new cases for Saturday. The district, Chaoyang, is home to 3.45 million people.

In Shanghai, images of workers in white hazmat suits sealing entrances of housing blocks and closing off entire streets with green fencing - roughly roughly two metres tall - went viral on social media, 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 from balconies at workers trying to set up fencing. The workers relented and took it away. Other videos showed people trying to pull fences down.

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

Many of the fences were erected around compounds designated "sealed areas" - buildings where at least one person tested positive for COVID-19, meaning residents are forbidden from leaving their front doors.

It was not clear what prompted authorities to resort to fencing. A notice dated Saturday from one local authority shared online said it was imposing "hard quarantine" in some areas.

Reuters was not able to verify the authenticity of the notice or all of the images, but saw green fencing on a street in central Shanghai on Sunday.

In recent days, Reuters has also seen police in hazmat suits patrolling Shanghai streets, setting up road blocks and asking pedestrians to return home.

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

MISERY

Shanghai is China's most populous city and most important economic hub. It is battling the country's biggest COVID-19 outbreak since the coronavirus first emerged in Wuhan in late 2019 with a policy that forces all positive cases into quarantine centres.

The lockdown, which for many residents has lasted over three weeks, has fuelled frustration over lost wages, family separation and quarantine conditions as well as access to medical care and food.

Supermarket Freshippo, backed by Alibaba Group Holding Ltd , said on Sunday it was adding couriers to meet demand in the city.