Tianjin reported 33 new positive cases of COVID-19 on Friday morning, bringing the total to 226 since the latest outbreak started in August.

"This round of pandemic has four sources, one of which is very closely related to a virus variant that recently spread in South Korea," said Han Jinyan, deputy director of the Tianjin health commission, during a news conference on Thursday.

As of 4 pm Thursday, a total of 200 positive cases have been linked to the same source, which is similar to the virus found in some early patients. Their homes had tainted South Korean food, she said.

"The gene sequencing from the virus in some cold chain food in their homes indicated that it was not much different from the recent strain that spread in South Korea," Han said.

Other sources included three patients who had close interaction with a tourist who had returned from Tibet autonomous region; some truck drivers from other provinces; and some patients infected with the BA.2.76 variant, which is not linked to those sources, according to epidemiologists.

"The virus has been transmitted to 51 streets and towns in 14 districts in the city," Han said. "This round of the pandemic has fast transmission speed and has been linked to major clusters, including some local soccer fields," she said.

Tianjin requires residents not to leave unless absolutely necessary. It postponed students' return to school on Thursday.

In addition, all museums, libraries, tourist attractions and entertainment venues were ordered to close on Friday. The government has instructed tourist agencies to refund to people who have arranged to come to Tianjin.

Traffic on some expressways will be regulated starting on Friday.