Shanghai authorities doubled down on their offensive against Covid-19 on Friday, launching a new round of city-wide testing and warning residents their three-week lockdown would only be lifted in batches once transmission is stamped out, Reuters reported.

The Shanghai government said on its official WeChat account, the city's epidemic was showing a "positive trend" and that life in the city could return to normal soon as long as people stuck to strict rules to curb the spread of Covid-19.

And while some Shanghai districts tightened restrictions on movement, officials in neighbourhoods that met criteria for people to be allowed to leave their homes were still preventing them from doing so, fuelling anger and frustration among residents who have endured weeks of lockdown.

"Our goal is to achieve community zero-Covid as soon as possible," the government said.

"This is an important indication that we win this major, hard battle against the epidemic ...so that we can restore normal production and life order."

Shanghai locked virtually all of its 25 million people into their homes at the start of April after infections began to surge. Residents have faced income losses, difficulty getting food, family separations and poor conditions in quarantine, according to Reuters.

Frustration with the rigid enforcement of draconian restrictions has reached new heights this week.

Health officials raised hopes for some return to normal by saying transmission had been curbed, only for city officials to pour cold water over such expectations as the highly-transmissible Omicron variant has proven hard to eliminate.

Late on Thursday, Shanghai announced a new round of "nine major" actions, including daily city-wide testing from Friday, accelerating transfers to quarantine centres, minimising people movement and ensuring enforcement of the rules, Reuters reported.