Sharjah24 – AFP: China placed all 17 million residents in one of its biggest cities under lockdown on Sunday, as virus cases doubled nationwide to nearly 3,400 and anxiety mounted over the resilience of its 'zero-Covid' approach in the face of the worst outbreak in two years.

The southern tech hub of Shenzhen told all residents to stay at home as the city struggles to eradicate an Omicron flare-up linked to neighbouring virus-ravaged Hong Kong.

The lockdown and a suspension of public transport will last until March 20, a city government notice said, adding that it would launch three rounds of mass testing.

The move extends an earlier lockdown imposed on the city's central business district.

Shenzhen reported 66 new infections on Sunday -- a fraction of the 32,430 confirmed the same day in Hong Kong.

The surge in infections across China has also prompted authorities to close schools in Shanghai and lock down multiple northeastern cities, as 18 provinces battle clusters of the Omicron and Delta variants.

China, where the virus was first detected in late 2019, has maintained a strict 'zero-Covid' policy enforced with 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 that approach.

Shanghai has so far been spared a citywide order to stay home, but individual housing compounds were being locked down as the megacity 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 also confined to their homes Sunday.

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.