Beijing launched mass Covid-19 testing in some areas on Friday, while Shanghai was testing all hospital staff as China battles its worst outbreak of the disease since March and families fret over reunion plans for the Lunar New Year amid new curbs.
Mainland China reported a slight decline in new daily Covid-19 cases on Friday - 103 from 144 cases a day earlier.
Of these new cases, 94 were local transmissions: northeastern Heilongjiang reported 47 new cases, while Jilin province reported 19 new cases. Shanghai reported six new cases, while the capital Beijing reported three new cases.
Some districts in Beijing launched mass Covid-19 tests following several consecutive days of new cases in the Chinese capital, with long queues forming in certain parts of the town.
Shanghai began testing all hospital staff for the disease on Thursday after two such 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 owned by a joint venture between Thailand's top agro-industrial conglomerate, CP Group, and a local development zone, according to a statement by local officials.
It is thought to be the first cluster of cases in a meat plant in China, although such facilities have been hotspots for pandemic outbreaks elsewhere in the world. The joint venture could not be immediately reached for comment.
Tens of millions of people have been under some kind of lockdown in northern cities amid worries that undetected infections could spread quickly during the Lunar New Year holiday, which is just weeks away.
Hundreds of millions of people usually travel during the holiday, in mid-February this year, as migrant workers return to their home provinces to see family. Officials expect large numbers of travellers, although much fewer than in normal years.
Hebei province, next to Beijing, reported 18 new locally transmitted cases. At the high speed railway station in its largest city Shijiazhuang, passengers were allowed to get off a train on Friday but none were seen getting on.
"I've never been separated from my daughter over New Year before," said a woman surnamed Hao, who is in Shijiazhuang taking care of her mother and has been told by her neighbourhood she is now not allowed to return to Beijing, where the rest of her family are.
Hao is hoping that restrictions will lift in time for them to reunite over the festival.
"When (my daughter) was studying abroad in London, I flew there on New Year's eve. She is my motivation to go back," she said. Hao's father is in a nursing home in Beijing which is no longer allowing visitors.
The capital's west train station, which normally sees vast numbers of passengers passing through in the run up to the Lunar New Year, was virtually empty on Friday morning.
A queue more than 200 meters long was seen outside Dengshikou Elementary School, a testing spot near the centre of the city.
A man surnamed Lin said the supermarket he works at had told him to take a test that morning.
"People here should all be organised by their companies," he said. "I'm not that worried, though this round of the outbreak is a bit unexpected. I came as my work unit told me to."
The number of new asymptomatic cases, which China does not classify as confirmed cases, rose to 119 from 113 cases a day earlier.
The total number of confirmed Covid-19 cases in Mainland China now stands at 88,804, while the death toll remained unchanged at 4,635.