A growing COVID-19 cluster in China’s Dalian has prompted the northeastern port city to restrict outbound travel, reduce offline school classes, and close a few cultural venues after being told by national authorities that the outbreak must be contained as soon as possible.

Dalian reported 52 locally transmitted infections with confirmed symptoms on Thursday, the most of any Chinese city affected in a nationwide outbreak that has been ongoing since mid-October, and more than doubling from 21 cases the day before, according to official data released on Friday.

Between October 17 and November 11, 1,149 local cases were discovered in China. While the number is small in comparison to many outbreaks outside the country, local authorities have expended resources to contain the outbreak, and Beijing is unlikely to change its zero-tolerance policy anytime soon.

“Various measures should be accelerated and improved in quality in order to bring the outbreak under control in a shorter period of time and to minimize the outbreak’s impact on manufacturing and public life,” the National Health Commission said on Thursday, citing a meeting chaired by the commission’s director in Dalian.

The number of people leaving Dalian has dropped by 96.5 percent to 918 per day on average, according to a local transportation official late Thursday, after the city of 7.5 million people imposed restrictions on public transportation and warned residents not to leave the city for unnecessary reasons.

The city has ordered that offline lessons be discontinued in kindergartens, primary and secondary schools, as well as a number of libraries and museums, and has launched a second round of city-wide mass testing.

On Friday, Dalian residents were urged not to leave their homes unless absolutely necessary.

According to the state-backed newspaper Global Times, Dalian, a major port for seafood shipments as well as fruit and some meats, has also ordered all businesses handling imported chilled and frozen foods to halt operations.

As of Nov. 11, mainland China had reported 98,099 confirmed symptomatic COVID-19 patients, including both domestic and international cases. The total number of deaths remained at 4,636.