BANGKOK--South Korea on Thursday reported its biggest jump in coronavirus cases in more than 50 days, a huge setback that could erase some of its hard-won gains. Health officials warned that the resurgence is getting harder to track and social distancing and other steps need to be taken.

The Korea Centers for Disease Control and Prevention said 67 of the 79 new cases reported were from the Seoul metropolitan area, where about half of South Korea’s 51 million people live.

Health Minister Park Neung-hoo during a virus meeting pleaded for all residents in the greater capital area to avoid unnecessary gatherings and urged companies to keep sick employees off work.

At least 69 infections so far have been linked to workers at a massive warehouse operated by local e-commerce giant Coupang. Health authorities say the company likely didn’t enforce preventive measures such as masks at the facility in Bucheon, near Seoul, and may have had employees working while they were sick.

Hundreds of other infections have been linked to nightclubs and other entertainment venues, which saw huge crowds in early May after officials relaxed social distancing guidelines.

It remains to be seen whether the recent spike in infections force back a phased reopening of schools, which had been a major accomplishment in the nation’s anti-virus campaign. The Education Ministry on Wednesday said class openings were delayed at 561 schools nationwide because of virus concerns.

KCDC director Jeong Eun-kyeong has said the country may need to reimpose social distancing restrictions after easing them in April, saying it’s becoming increasingly difficult for health workers to track transmissions amid increasing public activity.

“The number of people or locations we have to trace are increasing geometrically,” she said during a briefing Wednesday afternoon. “We will do our best to trace contacts and implement preventive measures, but there’s a limit to such efforts. There’s a need to maximize social distancing in areas where the virus is circulating, to force people to avoid public facilities and other crowded spaces.”

Officials are preparing for a possible surge of infections in the greater capital area, mapping out plans to share hospital capacities between Seoul and nearby cities and ensure swift transports of patients so that a spike of cases in one area doesn’t overwhelm its hospital system.

Meanwhile, South Korea’s central bank lowered its policy rate to an all-time low of 0.5 percent to soften the pandemic’s shock to the country’s trade-dependent economy. The Bank of Korea also adjusted its annual growth outlook from a 2.1 percent expansion to a 0.2 percent contraction. The country’s economy hasn’t seen an annual contraction since 1998. The nation’s economy shrank 1.4 percent during the first three months of the year as people stayed home and exports shrank amid worldwide lockdowns.

South Korea was reporting around 500 new cases per day in early March before managing to stabilize its outbreak with aggressive tracking and testing, which allowed officials to relax social distancing guidelines.

But Seoul and nearby cities restored some of the controls in recent weeks by shutting thousands of bars, karaoke rooms and other entertainment venues to slow the spread of the virus.

The country also began requiring masks on public transit and airline flights this week. Taxi drivers also were allowed to refuse passengers who weren’t wearing masks.

The spike Thursday followed 40 new cases reported Wednesday, which was the highest figure in 49 days. South Korea has now reported 11,344 cases and 269 deaths from COVID-19.

In other developments around the Asia-Pacific region:

BANGLADESH FIRE: A fire that swept through a hospital’s coronavirus unit in Bangladesh’s capital killed five people. Firefighters recovered the bodies of four men and one woman after the blaze was controlled, Dhaka fire agency official Quamrul Islam said. The United Hospital Ltd. is in Dhaka’s Gulshan area, where many diplomatic missions and corporate offices are located. Bangladesh on Wednesday had 38,292 coronavirus cases including 544 deaths.

CHINA’S CONGRESS NEARS CONCLUSION: China on Thursday announced two new cases of coronavirus, both from abroad, as it moves to close the annual session of its ceremonial legislature that had been delayed by the outbreak. No new deaths were reported and just 73 people remained in treatment, while another 518 remain under isolation and observation for either suspected of having the virus or testing positive without showing any symptoms. China has reported a total of 4,634 deaths from COVID-19 among 82,995 cases. The National People’s Congress is to conclude its meetings later Thursday.