Watch: China battles virus resurgance
China is battling its biggest coronavirus outbreak since March.
Measures are being taken across the nation to try to bring the renewed spread of infections under control.
Beijing launched mass COVID-19 testing on Friday and Shanghai is testing all hospital staff.
The outbreak comes less than a month before Chinese New Year - the most important event in China’s annual calendar which sees hundreds of millions travelling across the country, and celebrations in the streets.
Long queues formed in some districts in Beijing, where mass testing has been launched following several consecutive days of new cases.
City officials said there were some "leaks" in epidemic control in some rural areas, with inadequate adherance to rules on wearing masks, social distancing and temperature checks.
They have announced an ambitious programme to test two million people within 48 hours in an attempt to snuff out the new cluster of cases believed to be linked to a more contagious virus variant.
A queue more than 200 meters long built up outside Dengshikou Elementary School, a testing spot near the city center.
A man surnamed Lin said the supermarket he works at had told him to get a test.
"I'm not that worried though this round of the outbreak is a bit unexpected. I came as my work unit told me to," he said.
Shanghai began testing all hospital staff for the disease on Thursday after two workers tested positive.
Almost all of the local transmissions and asymptomatic cases in Harbin, the capital of Heilongjiang province, were linked to a meat processing plant.
While the number of cases is small compared to outbreaks in western countries, the flareup — fuelled by an unusually cold winter — is China’s biggest COVID challenge since the original outbreak in Wuhan when the threat of potential spread due to Chinese New Year celebrations is taken into account.
The total number of cases in Beijing stood at 23 on Wednesday, while over a thousand infections have been found nationwide since early January, mostly in China’s vast rural northern provinces.
Tens of millions of people have been under some form of lockdown in China’s northern cities amid worries that undetected infections could spread quickly during the Lunar New Year holiday in three week’s time.
Hundreds of millions of people usually travel during the holiday, as migrant workers return to their home provinces to see family.
China’s response to the first outbreak of the pandemic was strict. As soon as authorities accepted there was a problem - the severity of the spread was initially denied - they clamped down hard.
On 23 January 2020, two days before Chinese New Year, some 11 million people in Wuhan were put under tight quarantine, and face masks and social distancing became mandatory.
The methods used in Wuhan quickly followed in other major cities such as Beijing and Shanghai, with immediate lockdowns and swift mass testing being imposed.
Entry into China was managed by tight entry and quarantine control.
However, by August life was back to relative normality and pictures from Wuhan - thought to be the origin of the global outbreak - showed partygoers at nightclubs and at pop concerts.
While China's rigorous lockdowns initially struck observers as harsh and restrictive, the official data one year on showed a comparatively low death toll compared to the rest of the world.
The total number of confirmed COVID-19 cases in mainland China now stands at 88,804, while the death toll is 4,635.
In comparison, on Friday Britain had recorded 3.54 million cases, and more than 94,500 deaths.
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