An exterior view of MGM Cotai in Macau, China February 13, 2018. REUTERS/Bobby Yip/File Photo

Macau casino MGM Cotai, operated by MGM China (2282.HK), reopened on Wednesday after being sealed for three days after a dealer was found to be infected with COVID and authorities quarantined more than 1,500 people inside in response.

All of the people held in the casino resort in the Chinese special administrative region tested negative for the coronavirus and had been released, health authorities said, however they must take daily coronavirus tests.

The former Portuguese colony has discovered about a dozen coronavirus cases in the past week after having no cases for more than three months.

Macau closely follows China's "dynamic zero" coronavirus policy which seeks to immediately curb any outbreaks. Macau has an open border with the mainland and many cross back and forth from homes and jobs in the neighbouring city of Zhuhai.

A round of mass PCR tests of Macau's 700,000 people on Wednesday found all samples negative for the virus. Another round of mass tests will be conducted on Friday and Saturday, the government said.