BEIJING: Millions of people across China endured lockdowns on Sunday as virus cases doubled to nearly 3,400 and anxiety mounted over the resilience of the country's 'zero-Covid' approach in the face of the worst outbreak in two years.

The nationwide case surge has prompted authorities to close schools in Shanghai and lock down central neighbourhoods in southern tech powerhouse Shenzhen as well as whole northeastern cities, as almost 18 provinces battle clusters of the Omicron and Delta variants.

In China's most populous metropolis Shanghai, individual housing compounds were being locked down one by one as the city ramped up efforts to contain infections and test suspected close contacts.

Jilin -- the city at the centre of the outbreak in the northeast -- was partially locked down Saturday, while residents of Yanji, an urban area of nearly 700,000 bordering North Korea, were confined to their homes Sunday.

China, where the virus was first detected in late 2019, has maintained a strict 'zero-Covid' policy enforced by swift lockdowns, travel restrictions and mass testing when clusters have emerged.

But the latest flare-up, driven by the highly transmissible Omicron variant and a spike in asymptomatic cases, is testing the efficacy of that approach.

Zhang Yan, a Jilin health commission official, conceded that the response from local authorities had been lacking.

"The emergency response mechanism in some areas is not robust enough," he said at a Sunday press briefing.

"There is insufficient understanding of the characteristics of the Omicron variant... and judgment has been inaccurate."

Residents of Jilin have completed six rounds of mass testing, with the city reporting more than 2,200 cases of the Omicron variant since Saturday.

The neighbouring city of Changchun -- an industrial base of nine million people -- was locked down Friday, while at least three other small cities have been locked down since March 1.

China allows self-use COVID antigen tests as local cases hit two-year high

The mayor of Jilin and the head of the Changchun health commission were dismissed from their jobs Saturday, state media reported, in a sign of the pressure placed on local authorities to contain virus clusters.

Covid-zero?

But the strain is showing, with officials increasingly urging softer and more targeted measures to contain the virus, while economists warn tough clampdowns are hurting the economy.

In Shanghai, authorities have locked down a number of housing compounds -- with some residents told the measure will last two days -- as well as individual schools, businesses, restaurants and malls over close-contact fears.

Authorities also said Sunday that people cannot leave or enter the city without a negative test from the past 48 hours.

"I have friends who I hung out with a few days ago but were suddenly quarantined recently," Shanghai resident Serena Li told AFP.

The government's approach will "protect citizens", she said, adding: "In the long run, it's good."

Long lines were seen outside hospitals as people rushed to get tested.

"There's no other way. We definitely have to do what the government has arranged," said a data analytics worker surnamed Zhang.

In Shenzhen, the southern city of around 13 million bordering Hong Kong, residents are nervous over the renewed outbreak and swift, draconian measures to quash clusters.

"It's the worst since 2020," a Shenzhen resident surnamed Zhang told AFP. "The closures are too sudden, my friend woke up in the morning to find her building was sealed overnight without warning. Her boss had to mail her laptop to her."

The Shenzhen subdistrict of Futian, which is home to 300,000 people, was locked down Sunday. It shares a land border crossing with Hong Kong, where the caseload over recent weeks has soared, alarming officials in Beijing.

Hong Kong currently has one of the world's highest death rates from the virus, as the Omicron variant cuts through its elderly population among whom vaccine hesitancy proliferates.

As cases rise, China's National Health Commission announced Friday that it would make rapid antigen tests available for citizens to buy online or from clinics for "self-testing".

Although nucleic acid tests will continue to be the main method of testing, the move suggests China may be anticipating that official efforts will not be able to contain the virus.