Beihai city in the Guangxi Zhuang autonomous region reported 161 asymptomatic cases of COVID-19 on Thursday, increasing its total to 186 after the first case emerged on Tuesday, according to the city's Center for Disease Prevention and Control.

All the cases are asymptomatic, the center said.

With the number rising, Beihai — a tourism hot spot — has designated 86 areas as high risk and 70 areas of medium risk, according to officials at a news conference on Friday morning.

The first case in this round of epidemic in the city involved the Omicron BA.2.3 subvariant, which is not homologous with previous cases detected in Guangxi, an earlier news conference revealed.

The subvariant has the characteristics of strong infectivity, a short incubation period and strong concealment, with most infected people being asymptomatic, it added.

Beihai reported one asymptomatic case on Tuesday, 24 on Wednesday and 161 on Thursday — a rapid rise.

"The epidemic in Beihai is developing, with a high risk of further transmission," Lan Tianli, chairman of the Guangxi Zhuang autonomous region, said over a video link on Thursday. He ordered related departments to strictly and quickly implement all-around measures to curb the spread.

The city is carrying out heavy nucleic acid testing. As of Thursday, it had collected more than 1.35 million samples.

All scenic spots have been closed and temporary control measures were imposed in the main urban areas of Beihai on Wednesday.