Some residential compounds are being turned into quarantine centres.

Millions are confined to their homes as Shanghai battles a fresh outbreak of the virus. Anyone who tests positive is placed in quarantine.

But with more than 20,000 new cases a day, authorities are struggling to find enough space.

The city in recent weeks has converted exhibition halls and schools into quarantine centres, and set up makeshift hospitals.

The low numbers of serious cases in Shanghai have led some to ask whether a lockdown is necessary, correspondents say.

In recent weeks many residents have taken to social media to complain about the restrictions and the lack of food supplies.

People have to order in food and water and wait for government drop-offs of vegetables, meat and eggs, and analysts say many are running low on supplies.

The lockdown extension has overwhelmed delivery services, grocery shop websites and even the distribution of government supplies.

Three weeks into lockdown, some here in Shanghai are angry.

Head to toe in protective suits in an eastern district of the city, officers were forcing people out of their rented apartments so they could turn them into temporary quarantine facilities, all in the name of a war against a resurgent Covid.

But for some it was just too much, their homes sequestered, their desperation easy for all to hear.

A few miles away, there was an organised protest, a bold stand as the lockdown takes hold in a country where you can be arrested for picking quarrels.

They're angry about a local school being turned into another quarantine facility. Police with riot shields forced them off the streets in the end.

This was on a small scale but it's a sign of anger and frustration as this lockdown goes on.

Meanwhile the Chinese government has sent teams to the city to help more than 660 companies in key sectors of the economy such as semiconductor and car manufacturing to resume production, reports state media.

The Ministry of Industry and Information Technology said on Friday they would ensure the supply of medical goods and the smooth flow of supply chains.

The move follows reports that parts of China's manufacturing sector might soon have to close, at least temporarily, because companies cannot get essential components from Shanghai.

He Xiaopeng, president of electrical vehicle manufacturer XPeng, said that if work did not start again in Shanghai during May, potentially all car factories across the country might have to stop operating.

China is one of the last remaining nations still committed to eradicating Covid, in contrast to most of the world which is trying to live with the virus.

But this zero-Covid policy has come under strain in recent weeks with the spread of the Omicron variant.