Exposure to contaminated imported goods could be the cause of the latest coronavirus outbreak in Zhuhai, Guangdong province, according to local health authorities.

"Based on the epidemiological investigation and laboratory testing, exposure to contaminated imported goods is not excluded in the source of the latest COVID-19 outbreak," said Huang Yun, deputy director of the Zhuhai Municipal Health Commission.

As of Sunday, Zhuhai, in western Guangdong, has reported 12 locally transmitted confirmed cases and one asymptomatic carrier since a 53-year-old woman in the city first tested positive for COVID-19 on Friday.

According to Huang, the woman was engaged in a customer service job that required frequent contact with imported goods.

"We are stepping up efforts to investigate further and trace the cause for the outbreak," Huang said, adding that all cases detected so far in Zhuhai were the Omicron strain and were all in the same chain of transmission.

"The clinical manifestations of the Omicron strain are very different from the Delta strain. The symptoms of Omicron infection are relatively mild," she said.

However, the transmission of the Omicron strain is strong, with infection of more young people but fewer lung lesions, Huang said.

Yang Jian, chief physician of the respiratory department of the Zhuhai Municipal People's Hospital, said the contagiousness and replication rate of the Omicron strain are much higher than with the Delta strain.

"The difficulty of preventing the Omicron strain is much higher, given that it is more hidden and unpredictable," he said.