A city of 10 million people in China has imposed new lockdown measures to prevent the spread of coronavirus following a surge in cases.
Harbin now has China's biggest Covid-19 outbreak after the highly contagious virus was first detected in Wuhan late last year.
A new cluster of at least 70 cases has been linked to a 22-year-old student who unknowingly spread the killer bug after returning from New York, say officials.
The city was already battling a wave of new cases involving infected citizens who had arrived from neighbouring Russia.
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Harbin, the provincial capital of Heilongjiang and its biggest city, has banned entry to residential zones by non-locals and vehicles registered elsewhere, state media said.
It had already ordered isolation for those arriving from outside China or key epidemic areas.
Heilongjiang has been in the forefront of China's latest efforts to identify infected citizens arriving from Russia, with which it shares a border, to curb the spread of the virus.
"All confirmed cases, suspected cases, close contacts of asymptomatic people, and close contacts of close contacts should be quarantined and tested," state media cited the city government as saying.
Harbin said this month it was ordering 28 days of quarantine for all arrivals from abroad, with two nucleic acid tests and an antibody test for each.
It also set 14-day lockdowns for residences where confirmed and asymptomatic cases are found.
"I'm not taking my daughter or parents outside anymore. If we need any food or vegetables, we just let my husband buy it on his way back," said a 34-year-old Harbin resident surnamed Sun.
"And whenever anyone has to go outside, he or she will leave their shoes outside the door to avoid bringing back any virus."
Harbin, which has air links with Russia, reported seven new confirmed cases on Tuesday, taking its local infections to 52, excluding recoveries discharged from hospital.
Additionally, three infected travellers arrived from Russia. About 1,400 people are being observed for signs of the virus.
By Tuesday, Heilongjiang reported 537 local confirmed cases, including 470 discharged from hospital. Besides Harbin, the city of Mudanjiang has two current confirmed cases.
"Prevention measures have been more strict recently, and people from Mudanjiang or Harbin will not be allowed to come into our town," said a civil servant surnamed Zhang, who lives in Mishan town on the eastern edge of Heilongjiang.
One persisting cluster in Harbin centred on an 87-year-old man surnamed Chen who had stayed at two hospitals since April 2, four days after dinner at home with his son's friends, two of whom later tested positive.
By Tuesday, Chen had infected 78 people, with 55 confirmed, though 23 who tested positive have yet to show virus symptoms.
Those infected were mainly family members, hospital patients and their families, and doctors and nurses in direct or indirect contact, provincial health officials said.
Of seven new confirmed cases in Heilongjiang on Tuesday, four were patients who had stayed in the same ward as Chen, while three were healthcare workers at one hospital.
The virus that infected the cluster has travelled beyond the province, with health officials in neighbouring Liaoning reporting on April 16 a confirmed case whose father had stayed at the same hospital as Chen.
On Monday, the northern region of Inner Mongolia reported a confirmed case in an individual who had stayed at one of the Harbin hospitals at the same time as Chen and the Liaoning patient.
