China's southern city of Shenzhen on Monday shut down the world's largest electronics market. It suspended public transport nearby as authorities enforced neighbourhood-wide lockdowns in response to a small number of Covid cases.

Huaqiangbei, a busy shopping area home to thousands of stalls selling computer components, mobile phone parts and microchips, is among three neighbourhoods placed under a mandatory four-day lockdown in the Futian district, according to the district government.

Residents in those neighbourhoods are forbidden to leave their homes except for Covid testing, which they must undergo daily until Thursday. 

All businesses in the affected areas are shut down through Thursday, except for supermarkets, pharmacies and hospitals. Restaurant dining is also suspended, with only takeaways allowed.

China is one of the last places in the world still enforcing stringent zero-Covid measures, which rely on sweeping digital surveillance, mass testing, extensive quarantines and snap lockdowns.

On Tuesday, Shenzhen, an international technology hub of 18 million people, reported just 35 infections, including 11 asymptomatic cases.

The heavy-handed approach has seen dozens of neighbourhoods across Shenzhen identified as "high-risk areas" and placed under strict lockdown orders. Videos shared by residents on social media show metal barriers -- some topped with barbed wire -- erected outside residential buildings, blocking residents from leaving.

The districts of Luohu and Longgang also shut down all entertainment venues and public parks, and banned gatherings from conferences and performances to square dancing.

Authorities also suspended service at 24 subway stations and hundreds of bus stations across Shenzhen, including around the Huaqiangbei electronics market.

At a news conference Monday, Shenzhen officials said the outbreak is mainly driven by new subvariant Omicron BF.15, which they said is more transmittable and harder to detect.

"The upcoming period will be the most stressful, high-risk and grim period for epidemic prevention and control in our city," a Shenzhen official told the news conference.