This photo shows the workers in protective suits at lockdown areas in Shanghai. AFP

China reported 5,280 new Covid-19 cases on Tuesday, more than double the previous day's tally as the highly-transmissible Omicron variant spreads across a country which has tethered tightly to a 'zero-Covid' strategy.

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That approach, which pivots on hard localised lockdowns and has left China virtually cut off from the outside world for two years, appears to be on the line as Omicron finds its way into communities.

At least 13 cities nationwide were fully locked down on Tuesday, while various other cities had partial lockdowns.

Workers prepare a drone amid the snow to disinfect a residential compound under lockdown in Changchun. Reuters

The northeastern province of Jilin was the worst-hit, with over 3,000 new cases on Tuesday, according to the National Health Commission.

Residents of several cities there including the provincial capital of Changchun -- home to nine million people -- are under stay-at-home orders.

Shenzhen -- the southern tech hub of 17.5 million people -- is three days into a lockdown with many factories closed and supermarket shelves emptying, while China's largest city Shanghai is under a lattice of restrictions -- which fall short of a citywide shutdown.

But scenes of closed neighbourhoods, panic buying and police cordons cast back to the early phase of the pandemic, which first emerged in China in late 2019 but has eased in much of the rest of the world.

A worker in a protective suit collects a swab at a residential compound under lockdown in Shenzhen. Reuters

Tuesday was the sixth day in a row that more than 1,000 new cases were recorded in the world's second-biggest economy, with experts forecasting a dent to growth as the virus billows out.

"The recent Covid outbreak and renewed restrictions, notably the lockdown in Shenzhen, will weigh on consumption and cause supply disruptions in the near term," Tommy Wu, of Oxford Economics said in a briefing note.

He added it will be "challenging" for China to meet its official GDP growth target for the year of around 5.5 percent.

Hong Kong stocks plunged by more than three per cent Tuesday, extending the previous day's tech-fuelled rout.

Dozens of domestic flights at airports in Beijing and Shanghai were cancelled Tuesday morning, flight tracking data showed.

An outbreak at Volkswagen Group factories in the Jilin city of Changchun also prompted three sites to shut Monday for at least three days, according to a spokesman.

Police and workers are seen wearing protective clothes next to some lockdown areas in Shanghai. AFP

Various other cities including Shanghai have sealed off certain neighbourhoods and buildings, as authorities have sought to minimise disruption to daily life.

A top Chinese medical expert Zhang Wenhong has raised the prospect of softening the "zero-Covid" strategy in the face of the Omicron variant. But in the short term, he warned any relaxation of mass testing and lockdowns was impossible.

Health officials also say tighter restrictions could be on the way.

Jilin's governor vowed to go all-out to "achieve community zero-Covid in a week" during an emergency meeting Monday night, state media reported.

Residents of Jilin, which is on the border with North Korea, were banned from travelling out of and around the province Monday.

Agence France-Presse