CNN  — 

Until last week, Beijing seemed to have all but moved on from the coronavirus pandemic.

For 55 days, the Chinese capital had not reported any locally transmitted infections and life had been returning to normal. Businesses and schools reopened, people went back to work, and the city’s public transports and parks were once again teeming with crowds.

But that facade of normality was shattered last week, when a fresh cluster of coronavirus cases emerged from a sprawling wholesale food market in the city, infecting more than 180 people as of Friday.

Within a matter of days, the metropolis of more than 20 million people was placed under a partial lockdown. Authorities reintroduced restrictive measures used earlier to fight the initial wave of infections, sealing off residential neighborhoods, closing schools and barring hundreds of thousands of people deemed at risk of contracting the virus from leaving the city. Some 356,000 people have been tested in just five days.

People who have had contact with the Xinfadi market line up for coronavirus tests at a testing center on June 17.

The flare-up of infections in Beijing, the seat of Communist Party power and previously considered among the country’s safest cities, is a stark reminder of how easily the virus can come back to haunt places where it was thought to have been tamed.

Five days before the onset of the current outbreak, Beijing authorities had just downgraded the city’s four-tier public health emergency response alert level from Level 2 to Level 3. It was raised back to Level 2 on Tuesday night.

Similar cautionary tales have occurred repeatedly in recent months, with governments rushing to contain reemerging outbreaks after having seemingly brought initial infection numbers under control.

South Korea, much hailed for its success in containing the virus, has been fighting a spike in infections since late May after the easing of social distancing rules and the reopening of schools. Singapore had been considered a coronavirus success story until a wave of infections broke out in April among migrant workers living in packed dormitories.